Throw an explicit error to make it clear we don't support the TRIGGER combination of SELECT and FOR EACH ROW

Apply #418: MySQL compatibility: support for ALTER TABLE tbl_name MODIFY [COLUMN] col_name column_definition, patch from Ville Koskela.

Expose limit/offset/distinct/having/group values as getter methods on Query for external TableEngine implementations

suggestion from markaddleman@gmail.com

--no commit message