Make all opcode constants to have type byte

It was probably a thinko in d00e99e7 (Add more opcodes so we can read
Graphite's Carbon stream) which changed opcodes from string ("X") to
character ('X') constants and marked the first opcode with byte type,
probably with the idea that following opcodes will have the same type.

Unfortunately it is not so as the following program demonstrates:

	package main

	const (
	        opAAA byte = 'a'
	        opBBB      = 'b'
	)

	func main() {
	        op := opBBB
	        if true {
	                op = opAAA	// <-- line 11
	        }
	        println(op)
	}

	--> ./bc.go:11:6: cannot use opAAA (type byte) as type rune in assignment

Similarly if we try comparing opcodes, it also results in compile error:

	func main() {
	        op := opBBB
	        if op == opAAA {	// <-- line 10
	                panic(0)
	        }
	        println(op)
	}

	--> ./bc.go:10:8: invalid operation: op == opAAA (mismatched types rune and byte)

Since in the following patches it will be handy for encoder to e.g. set default
opcode first, and then change it under some conditions to another opcode,
exactly the same compile error(s) will pop up.

So let's fix all opcode constants to have their type as byte to avoid such
unexpected errors.

ogorek.go

@@ -19,70 +19,70 @@ import (
 // Opcodes
 const (
 	opMark           byte = '(' // push special markobject on stack
-	opStop                = '.' // every pickle ends with STOP
-	opPop                 = '0' // discard topmost stack item
-	opPopMark             = '1' // discard stack top through topmost markobject
-	opDup                 = '2' // duplicate top stack item
-	opFloat               = 'F' // push float object; decimal string argument
-	opInt                 = 'I' // push integer or bool; decimal string argument
-	opBinint              = 'J' // push four-byte signed int
-	opBinint1             = 'K' // push 1-byte unsigned int
-	opLong                = 'L' // push long; decimal string argument
-	opBinint2             = 'M' // push 2-byte unsigned int
-	opNone                = 'N' // push None
-	opPersid              = 'P' // push persistent object; id is taken from string arg
-	opBinpersid           = 'Q' //  "       "         "  ;  "  "   "     "  stack
-	opReduce              = 'R' // apply callable to argtuple, both on stack
-	opString              = 'S' // push string; NL-terminated string argument
-	opBinstring           = 'T' // push string; counted binary string argument
-	opShortBinstring      = 'U' //  "     "   ;    "      "       "      " < 256 bytes
-	opUnicode             = 'V' // push Unicode string; raw-unicode-escaped"d argument
-	opBinunicode          = 'X' //   "     "       "  ; counted UTF-8 string argument
-	opAppend              = 'a' // append stack top to list below it
-	opBuild               = 'b' // call __setstate__ or __dict__.update()
-	opGlobal              = 'c' // push self.find_class(modname, name); 2 string args
-	opDict                = 'd' // build a dict from stack items
-	opEmptyDict           = '}' // push empty dict
-	opAppends             = 'e' // extend list on stack by topmost stack slice
-	opGet                 = 'g' // push item from memo on stack; index is string arg
-	opBinget              = 'h' //   "    "    "    "   "   "  ;   "    " 1-byte arg
-	opInst                = 'i' // build & push class instance
-	opLongBinget          = 'j' // push item from memo on stack; index is 4-byte arg
-	opList                = 'l' // build list from topmost stack items
-	opEmptyList           = ']' // push empty list
-	opObj                 = 'o' // build & push class instance
-	opPut                 = 'p' // store stack top in memo; index is string arg
-	opBinput              = 'q' //   "     "    "   "   " ;   "    " 1-byte arg
-	opLongBinput          = 'r' //   "     "    "   "   " ;   "    " 4-byte arg
-	opSetitem             = 's' // add key+value pair to dict
-	opTuple               = 't' // build tuple from topmost stack items
-	opEmptyTuple          = ')' // push empty tuple
-	opSetitems            = 'u' // modify dict by adding topmost key+value pairs
-	opBinfloat            = 'G' // push float; arg is 8-byte float encoding
+	opStop           byte = '.' // every pickle ends with STOP
+	opPop            byte = '0' // discard topmost stack item
+	opPopMark        byte = '1' // discard stack top through topmost markobject
+	opDup            byte = '2' // duplicate top stack item
+	opFloat          byte = 'F' // push float object; decimal string argument
+	opInt            byte = 'I' // push integer or bool; decimal string argument
+	opBinint         byte = 'J' // push four-byte signed int
+	opBinint1        byte = 'K' // push 1-byte unsigned int
+	opLong           byte = 'L' // push long; decimal string argument
+	opBinint2        byte = 'M' // push 2-byte unsigned int
+	opNone           byte = 'N' // push None
+	opPersid         byte = 'P' // push persistent object; id is taken from string arg
+	opBinpersid      byte = 'Q' //  "       "         "  ;  "  "   "     "  stack
+	opReduce         byte = 'R' // apply callable to argtuple, both on stack
+	opString         byte = 'S' // push string; NL-terminated string argument
+	opBinstring      byte = 'T' // push string; counted binary string argument
+	opShortBinstring byte = 'U' //  "     "   ;    "      "       "      " < 256 bytes
+	opUnicode        byte = 'V' // push Unicode string; raw-unicode-escaped"d argument
+	opBinunicode     byte = 'X' //   "     "       "  ; counted UTF-8 string argument
+	opAppend         byte = 'a' // append stack top to list below it
+	opBuild          byte = 'b' // call __setstate__ or __dict__.update()
+	opGlobal         byte = 'c' // push self.find_class(modname, name); 2 string args
+	opDict           byte = 'd' // build a dict from stack items
+	opEmptyDict      byte = '}' // push empty dict
+	opAppends        byte = 'e' // extend list on stack by topmost stack slice
+	opGet            byte = 'g' // push item from memo on stack; index is string arg
+	opBinget         byte = 'h' //   "    "    "    "   "   "  ;   "    " 1-byte arg
+	opInst           byte = 'i' // build & push class instance
+	opLongBinget     byte = 'j' // push item from memo on stack; index is 4-byte arg
+	opList           byte = 'l' // build list from topmost stack items
+	opEmptyList      byte = ']' // push empty list
+	opObj            byte = 'o' // build & push class instance
+	opPut            byte = 'p' // store stack top in memo; index is string arg
+	opBinput         byte = 'q' //   "     "    "   "   " ;   "    " 1-byte arg
+	opLongBinput     byte = 'r' //   "     "    "   "   " ;   "    " 4-byte arg
+	opSetitem        byte = 's' // add key+value pair to dict
+	opTuple          byte = 't' // build tuple from topmost stack items
+	opEmptyTuple     byte = ')' // push empty tuple
+	opSetitems       byte = 'u' // modify dict by adding topmost key+value pairs
+	opBinfloat       byte = 'G' // push float; arg is 8-byte float encoding
 
 	opTrue  = "I01\n" // not an opcode; see INT docs in pickletools.py
 	opFalse = "I00\n" // not an opcode; see INT docs in pickletools.py
 
 	// Protocol 2
 
-	opProto    = '\x80' // identify pickle protocol
-	opNewobj   = '\x81' // build object by applying cls.__new__ to argtuple
-	opExt1     = '\x82' // push object from extension registry; 1-byte index
-	opExt2     = '\x83' // ditto, but 2-byte index
-	opExt4     = '\x84' // ditto, but 4-byte index
-	opTuple1   = '\x85' // build 1-tuple from stack top
-	opTuple2   = '\x86' // build 2-tuple from two topmost stack items
-	opTuple3   = '\x87' // build 3-tuple from three topmost stack items
-	opNewtrue  = '\x88' // push True
-	opNewfalse = '\x89' // push False
-	opLong1    = '\x8a' // push long from < 256 bytes
-	opLong4    = '\x8b' // push really big long
+	opProto    byte = '\x80' // identify pickle protocol
+	opNewobj   byte = '\x81' // build object by applying cls.__new__ to argtuple
+	opExt1     byte = '\x82' // push object from extension registry; 1-byte index
+	opExt2     byte = '\x83' // ditto, but 2-byte index
+	opExt4     byte = '\x84' // ditto, but 4-byte index
+	opTuple1   byte = '\x85' // build 1-tuple from stack top
+	opTuple2   byte = '\x86' // build 2-tuple from two topmost stack items
+	opTuple3   byte = '\x87' // build 3-tuple from three topmost stack items
+	opNewtrue  byte = '\x88' // push True
+	opNewfalse byte = '\x89' // push False
+	opLong1    byte = '\x8a' // push long from < 256 bytes
+	opLong4    byte = '\x8b' // push really big long
 
 	// Protocol 4
-	opShortBinUnicode = '\x8c' // push short string; UTF-8 length < 256 bytes
-	opStackGlobal     = '\x93' // same as OpGlobal but using names on the stacks
-	opMemoize         = '\x94' // store top of the stack in memo
-	opFrame           = '\x95' // indicate the beginning of a new frame
+	opShortBinUnicode byte = '\x8c' // push short string; UTF-8 length < 256 bytes
+	opStackGlobal     byte = '\x93' // same as OpGlobal but using names on the stacks
+	opMemoize         byte = '\x94' // store top of the stack in memo
+	opFrame           byte = '\x95' // indicate the beginning of a new frame
 )
 
 var errNotImplemented = errors.New("unimplemented opcode")