sql/sp_head.cc:
  Init. the simple_case flag.
sql/sp_head.h:
  New flag for (simple)case parsing.
sql/sp_pcontext.cc:
  Removed push_gen_label method (not needed any more).
sql/sp_pcontext.h:
  Removed push_gen_label method (not needed any more).
  Fixed bug in pop().
sql/sql_yacc.yy:
  Added CASE parsing.