Merged the different find_xxxx_table_in_list functions to one + some inline functions

Bug in diff_handlers and diff_cursors made it attempt to pop
the wrong number at jumps sometimes.

into pcgem.rdg.cyberkinetica.com:/usr/home/acurtis/work/mysql-5.0

Putting initialization into .cc will reduce compiler's abilities
to optimize this constant away.
Defines are not OK as they bloat global namespace.
Looking for a way to declare an efficient named constant in reduced
namespace (i. e. in  a class).
Let's try enums: normally they should be implicitly casted to int.
Let's see if we really have a compiler which won't do that.

into sanja.is.com.ua:/home/bell/mysql/bk/work-5.0

fixed other Item_ref methods where result_field involved

into mysql.com:/home/pem/work/mysql-5.0-merge

This finishes (almost) WL#2002: Implement stored procedure GOTO.
Only the syntax issue for free labels remains ("label L;" vs "L:").

into sanja.is.com.ua:/home/bell/mysql/bk/work-5.0

items for functions which is converted to constants internally to support its correct printing added (BUG#4663)

and BUG#336: Subselects with tables does not work as values for
local SP variables (which was closed before with a temp. fix, but not
actually fixed).

into mysql.com:/home/pem/work/mysql-5.0-merge

unions (crashed randomly), and made "label" not a reserved word.

into sanja.is.com.ua:/home/bell/mysql/bk/work-5.0

  Fix mysql-test failure in the 5.0 tree on Aug 23: label seems to be a reserved word in 5.0, and we to use it a s a column name we must but it inside backticks

into mysql.com:/home/pem/work/mysql-5.0-merge

Mostly done, it works, but the temporary LABEL syntax still to be fixed.