optimizer should check for "field LIKE const" not "field like STRING"

.bzrignore

@@ -528,3 +528,5 @@ support-files/MacOSX/Info.plist
 support-files/MacOSX/StartupParameters.plist
 support-files/MacOSX/postinstall
 support-files/MacOSX/preinstall
+configure.lineno
+innobase/configure.lineno

mysql-test/r/func_like.result

 drop table if exists t1;
 create table t1 (a varchar(10), key(a));
 insert into t1 values ("a"),("abc"),("abcd"),("hello"),("test");
+explain select * from t1 where a like 'abc%';
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	range	a	a	11	NULL	1	Using where; Using index
+explain select * from t1 where a like concat('abc','%');
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	range	a	a	11	NULL	1	Using where; Using index
 select * from t1 where a like "abc%";
 a
 abc
 abcd
+select * from t1 where a like concat("abc","%");
+a
+abc
+abcd
 select * from t1 where a like "ABC%";
 a
 abc

mysql-test/t/func_like.test

@@ -5,7 +5,10 @@
 drop table if exists t1;
 create table t1 (a varchar(10), key(a));
 insert into t1 values ("a"),("abc"),("abcd"),("hello"),("test");
+explain select * from t1 where a like 'abc%';
+explain select * from t1 where a like concat('abc','%');
 select * from t1 where a like "abc%";
+select * from t1 where a like concat("abc","%");
 select * from t1 where a like "ABC%";
 select * from t1 where a like "test%";
 select * from t1 where a like "te_t";

sql/item_cmpfunc.cc

@@ -1409,12 +1409,16 @@ longlong Item_func_like::val_int()
 
 Item_func::optimize_type Item_func_like::select_optimize() const
 {
-  if (args[1]->type() == STRING_ITEM)
+  if (args[1]->const_item())
   {
-    if (((Item_string *) args[1])->str_value[0] != wild_many)
+    String* res2= args[1]->val_str((String *)&tmp_value2);
+
+    if (!res2)
+      return OPTIMIZE_NONE;
+
+    if (*res2->ptr() != wild_many)
     {
-      if ((args[0]->result_type() != STRING_RESULT) ||
-	  ((Item_string *) args[1])->str_value[0] != wild_one)
+      if (args[0]->result_type() != STRING_RESULT || *res2->ptr() != wild_one)
 	return OPTIMIZE_OP;
     }
   }