Fix parsing of mysql client commands, especially in relation to
single-line comments when --comments was specified.

This is a little tricky, because we need to allow single-line
comments in the middle of statements, but we don't want to allow
client commands in the middle of statements. So in
comment-preservation mode, we go ahead and send single-line
comments to the server immediately when we encounter them on their
own. 

This is still slightly flawed, in that it does not handle a
single-line comment with leading spaces, followed by a client-side
command when --comment has been enabled. But this isn't a new
problem, and it is quite an edge condition. Fixing it would require
a more extensive overall of how the mysql client parses commands. 

Merge from 5.0-bugteam. Additional fix for unused ret variable warning.

BUG#38826

mysql-test/t/partition_innodb_stmt.test:
  post push fix for test case for bug#39084.
  
  (must have partitioning...)

Added KEY_BLOCK_SIZE option to I_S.TABLES.CREATE_OPTIONS field


mysql-test/r/information_schema.result:
  test result
mysql-test/t/information_schema.test:
  test case
sql/sql_show.cc:
  Added KEY_BLOCK_SIZE option to I_S.TABLES.CREATE_OPTIONS field

Bug#37671 crash on prepared statement + cursor + geometry + too many open files!
if mysql_execute_command() returns error then free materialized_cursor object.
is_rnd_inited is added to satisfy rnd_end() assertion
(handler may be uninitialized in some cases)


sql/sql_cursor.cc:
  if mysql_execute_command() returns error then free materialized_cursor object.
  is_rnd_inited is added to satisfy rnd_end() assertion
  (handler may be uninitialized in some cases)
sql/sql_select.cc:
  added result check
tests/mysql_client_test.c:
  test case

Removed values with more than 15 significant digits from the test case. Results of 
reading/printing such values using system library functions depend on implementation 
and thus are not portable.

mysql-test/r/type_float.result:
  Removed values with more than 15 significant digits from the test case.
mysql-test/t/type_float.test:
  Removed values with more than 15 significant digits from the test case.

Problem:
 XML syntax parser allowed to use quoted strings as attribute names,
 and tried to put them into parser state stack instead of identifiers.
 After that parser failed, if quoted string contained some slash characters.
Fix:
 - Disallowing quoted strings in regular tags.
 - Allowing quoted string in DOCTYPE declararion, but
 don't push it into parse state stack (just skip it).

Field_varstring::store
      
The code that temporary saved the bitmaps of the read set and the write set so that
it can set it to all columns for debug purposes was not expecting that the
table->read_set and table->write_set can be the same. And was always saving both in 
sequence.
As a result the original value was never restored.
Fixed by saving & restoring the original value only once if the two sets are the
same (in a special set of functions).

mysql-test/r/select.result:
  Bug #37936: test case
mysql-test/t/select.test:
  Bug #37936: test case
sql/item_cmpfunc.cc:
  Bug #37936: don't save/restore twice if the read and write sets are the same
sql/opt_range.cc:
  Bug #37936: don't save/restore twice if the read and write sets are the same
sql/table.h:
  Bug #37936: Make a designated set of functions that save/restore
  both the read and the write sets in a single call.

no conflicts

mysql-test/suite/parts/r/partition_bit_innodb.result:
  updated test result
mysql-test/suite/parts/r/partition_bit_myisam.result:
  updated test result