Bug 33983 (Stored Procedures: wrong end <label> syntax is accepted)

The server used to crash when REPEAT or another control instruction
was used in conjunction with labels and a LEAVE instruction.

The crash was caused by a missing "pop" of handlers or cursors in the
code representing the stored program. When executing the code in a loop,
this missing "pop" would result in a stack overflow, corrupting memory.

Code generation has been fixed to produce the missing h_pop/c_pop
instructions.

Also, the logic checking that labels at the beginning and the end of a
statement are matched was incorrect, causing Bug 33983.
End labels, when used, must match the label used at the beginning of a block.

into  bodhi.(none):/opt/local/work/mysql-5.0-runtime

into  whalegate.ndb.mysql.com:/home/tomas/mysql-5.0-ndb-merge

into  station.:/mnt/raid/alik/MySQL/devel/5.0-rt

into  whalegate.ndb.mysql.com:/home/tomas/mysql-5.0-ndb-merge

into  whalegate.ndb.mysql.com:/home/tomas/mysql-5.0-ndb-merge

- during commit deadlock timeout needs to be at least 5 times db hearbeat

into  whalegate.ndb.mysql.com:/home/tomas/mysql-5.0-ndb-merge

into  whalegate.ndb.mysql.com:/home/tomas/mysql-5.0-ndb-merge

into  mysql.com:/home/gluh/MySQL/Merge/5.0-opt

into  mysql.com:/home/gluh/MySQL/Merge/5.0-opt

into  mysql.com:/home/psergey/mysql-5.0-bug32198

- Make conditions like "date_col $CMP$ 'datetime-const'" range-sargable

into  mysql.com:/home/gluh/MySQL/Merge/4.1-opt

into  station.:/mnt/raid/alik/MySQL/devel/5.0-rt

Fixed case of comment.

into  bodhi.(none):/opt/local/work/mysql-5.0-runtime

into  stella.local:/home2/mydev/mysql-5.0-axmrg

into  whalegate.ndb.mysql.com:/home/tomas/mysql-5.0-ndb

into  stella.local:/home2/mydev/mysql-5.0-axmrg

into  adventure.(none):/home/thek/Development/cpp/mysql-5.0-runtime

into  pippilotta.erinye.com:/shared/home/df/mysql/build/mysql-5.0-build

into  pippilotta.erinye.com:/shared/home/df/mysql/build/mysql-5.0-build

into  pippilotta.erinye.com:/shared/home/df/mysql/build/mysql-5.0-build

into  pippilotta.erinye.com:/shared/home/df/mysql/build/mysql-4.1-build

into  whalegate.ndb.mysql.com:/home/tomas/mysql-5.0-ndb-merge

into  whalegate.ndb.mysql.com:/home/tomas/mysql-5.0-ndb-merge

with a fix for bug 32694. 

into  olga.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug27545

into  olga.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug32815

  
The problem was that when convert_constant_item is called for subqueries,
this happens when we already started executing the top-level query, and
the field argument of convert_constant_item pointed to a valid table row.
In turn convert_constant_item used the field buffer to compute the value
of its item argument. This copied the item's value into the field,
and made equalities with outer references always true.
  
The fix saves/restores the original field's value when it belongs to an
outer table.

Both arguments of the function NAME_CONST must be constant expressions.
This constraint is checked in the Item_name_const::fix_fields method. 
Yet if the argument of the function was not a constant expression no
error message was reported. As a result the client hanged waiting for a
response.
Now the function Item_name_const::fix_fields reports an error message
when any of the additional context conditions imposed on the function
NAME_CONST is not satisfied.