sql/sql_class.h:
  Made some temporary changes for UNION's. Still waiting for Monty's 
  comments on this.
sql/sql_delete.cc:
  Added a comment as Monty suggested
sql/sql_parse.cc:
  Some speedups for UNIONs
sql/sql_unions.cc:
  First attempts at running UNION's. 
  
  Removed header temporarily because of some bug in my pre-processor.