(BUG 8216)


mysql-test/r/group_by.result:
  New test case
mysql-test/r/user_var.result:
  Test changed (to be more correct) with bug fix
mysql-test/t/group_by.test:
  Added test for HAVING bug
sql/item_cmpfunc.cc:
  Fixed bug in HAVING when refering to RAND()
sql/item_func.cc:
  Fixed bug in HAVING when refering to RAND()
sql/item_row.cc:
  Fixed bug in HAVING when refering to RAND()
sql/item_strfunc.cc:
  Fixed bug in HAVING when refering to RAND()
sql/unireg.h:
  Added PSEUDO_TABLES_BITS for easy testing of real table reference