Code clean-up
sql_union.cc, union.test, union.result:
  A fix for a bug #978.
  This enables that NULL's can be entered into UNION's result set,
  although first SELECT columns are NOT NULL.
  This is also a start of fixing UNION's properly regarding type
  acceptance.
sql_select.cc:
  A commit for my second July SPRINT task

and result types

into bar.mysql.r18.ru:/usr/home/bar/mysql-4.1

into gluh.mysql.r18.ru:/home/gluh/mysql-4.1.DTFUNC

Test suit was extended to conver various arguments mixes.

into ice.snake.net:/Users/paul/mysql-4.1

into bar.mysql.r18.ru:/usr/home/bar/mysql-4.1

into eagle.mysql.r18.ru:/home/vva/work/mysql.orig/test/mysql-4.1

This allowed to reuse a lot of code. 

into bar.mysql.r18.ru:/usr/home/bar/mysql-4.1

  Stupid bug fix

as [skipped], even when run explicitly.)

into ice.snake.net:/Users/paul/mysql-4.1

args[0] is used instead. This allowed to resuse a lot of code.

into ice.snake.net:/Users/paul/mysql-4.1

into bar.mysql.r18.ru:/usr/home/bar/mysql-4.1

into mysql.r18.ru:/usr/home/ram/work/4.1

It's now passed as args[0]. This fix allowed to resuse a lot of code.

into mysql.r18.ru:/usr/home/ram/work/4.1

into teton.kitebird.com:/home/paul/mysql-4.1

into myvenu.com:/home/venu/work/sql/dev-4.1

if some of the arguments is STRING_RESULT the STRING_RESULT
else if some of the arguments is REAL_RESULT then REAL_RESULT
else INT_RESULT 

into sergbook.mylan:/usr/home/serg/Abk/mysql-4.1

into myvenu.com:/home/venu/work/sql/dev-4.1