merge fixes

into  dl145s.mysql.com:/data/bk/team_tree_merge/MERGE/mysql-5.0-opt

into  mysql.com:/home/hf/work/21790/my50-21790

into  mysql.com:/home/hf/work/19491/my50-19491

 The parser is allocating Item_field for references by name in ORDER BY
 expressions. Such expressions however may point not only to Item_field 
 in the select list (or to a table column) but also to an arbitrary Item. 
 This causes Item_field::fix_fields to throw an error about missing 
 column.
 The fix substitutes Item_field for the reference with an Item_ref when 
 not pointing to Item_field.

into  rurik.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug21727

into  mysql.com:/home/hf/work/mysql-5.0.19491

This is a performance issue for queries with subqueries evaluation
of which requires filesort.
Allocation of memory for the sort buffer at each evaluation of a
subquery may take a significant amount of time if the buffer is rather big.
With the fix we allocate the buffer at the first evaluation of the
subquery and reuse it at each subsequent evaluation.

into  mysql.com:/home/psergey/mysql-5.0-bug8804-r4

- Better comments
- Remove redundant and dead code.

the fix. 

Evaluate "NULL IN (SELECT ...)" in a special way: Disable pushed-down 
conditions and their "consequences": 
 = Do full table scans instead of unique_[index_subquery] lookups.
 = Change appropriate "ref_or_null" accesses to full table scans in
   subquery's joins.
Also cache value of NULL IN (SELECT ...) if the SELECT is not correlated 
wrt any upper select.

into  mysql.com:/usersnfs/abotchkov/mysql-5.0-opt1

into  rakia.gmz:/home/kgeorge/mysql/autopush/B21809-5.0-opt

into  rakia.gmz:/home/kgeorge/mysql/autopush/B23184-5.0-opt

 Item::val_xxx() may be called by the server several times at execute time 
 for a single query. Calls to val_xxx() may be very expensive and sometimes
 (count(distinct), sum(distinct), avg(distinct)) not possible.
 To avoid that problem the results of calculation for these aggregate 
 functions are cached so that val_xxx() methods just return the calculated 
 value for the second and subsequent calls.

into  mysql.com:/usersnfs/abotchkov/mysql-4.1-opt1

into  mysql.com:/usersnfs/abotchkov/mysql-5.0-opt1

into  mysql.com:/home/hf/work/current_stmt/my50-current_stmt

into  mysql.com:/home/hf/work/0current_stmt/my41-current_stmt

into  mysql.com:/home/hf/work/current_stmt/my50-current_stmt

            select OK.
The SQL parser was using Item::name to transfer user defined function attributes
to the user defined function (udf). It was not distinguishing between user defined 
function call arguments and stored procedure call arguments. Setting Item::name 
was causing Item_ref::print() method to print the argument as quoted identifiers 
and caused views that reference aggregate functions as udf call arguments (and 
rely on Item::print() for the text of the view to store) to throw an undefined 
identifier error.
Overloaded Item_ref::print to print aggregate functions as such when printing
the references to aggregate functions taken out of context by split_sum_func2()
Fixed the parser to properly detect using AS clause in stored procedure arguments
as an error.
Fixed printing the arguments of udf call to print properly the udf attribute.

the incompatibility was caused by current_stmt member added to the MYSQL
structure.
It's possible to move it to THD structure instead which saves ABI

into  mysql.com:/home/hf/work/w3475/my50-w3475

into  mysql.com:/home/hf/work/w3475/my41-w3475

into  mysql.com:/home/hf/work/w3475/my50-w3475

into  mysql.com:/home/hf/work/w3475/my50-w3475

Necessary code added to mysqltest.c.
Disabled tests are available now.

into  rurik.mysql.com:/home/igor/mysql-5.0-opt

into  rurik.mysql.com:/home/igor/mysql-4.1-opt

into  rurik.mysql.com:/home/igor/mysql-5.0-opt

into  dl145s.mysql.com:/data/bk/team_tree_merge/MERGE/mysql-5.0-opt

into  dl145s.mysql.com:/data/bk/team_tree_merge/MERGE/mysql-5.0-opt

into  dl145s.mysql.com:/data/bk/team_tree_merge/MERGE/mysql-4.1-opt