changes. This is mostly a merge between my repository and central 
one, so that I can take a test for multi table delete and fix it.


sql/mysql_priv.h:
  Added new functions needed for UNIONS, EXCEPT's etc
sql/sql_class.h:
  A little change in multi_delete class
sql/sql_lex.h:
  Added command for UNION's
sql/sql_parse.cc:
  One new function and SQLCOM_UNION_SELECT.
  
  Please do not test UNION's. This is just a start of the work on them
sql/sql_yacc.yy:
  Parsing stuff for the UNION's