the READ_ONLY global variable now allows statements which are to update only temporary tables
(note: if a statement, after parse stage, looks like it will update a non-temp table, it will be rejected,
even if at execution it would have turned out that 0 rows would be updated; for example
UPDATE my_non_tem_table SET a=1 WHERE 1 = 0; will be rejected).


sql/sql_parse.cc:
  The READ_ONLY global variable now allows statements which are to update only temporary tables
  (note: if a statement, after parse stage, looks like it will update a non-temp table, it will be rejected,
  even if at execution it would have turned out that 0 rows would be updated; for example
  UPDATE my_non_tem_table SET a=1 WHERE 1 = 0; will be rejected).
mysql-test/r/read_only.result:
  result for new test
mysql-test/t/read_only.test:
  test for READ_ONLY (there was none!) and for the new behaviour of READ_ONLY