sql/item_create.cc:
  specify cause of uncachability
sql/item_func.cc:
  specify cause of uncachability
sql/item_subselect.cc:
  fixed setting RAND_TABLE_BIT
  specify cause of uncachability
sql/item_subselect.h:
  used one field for all uncachability causes
sql/mysql_priv.h:
  causes of uncachability
sql/sql_lex.cc:
  specify cause of uncachability
sql/sql_lex.h:
  used one field for all uncachability causes
sql/sql_select.cc:
  used one field for all uncachability causes
sql/sql_union.cc:
  used one field for all uncachability causes
sql/sql_yacc.yy:
  specify cause of uncachability