[ticket/11538] Add unit tests for phpbb_validate_hex_colour().

PHPBB3-11538
[ticket/11538] Compare to '' instead of using empty(), so '0' does not pass.

PHPBB3-11538
[ticket/11538] Cut functional tests down a bit as these are more expensive.

PHPBB3-11538
Merge remote-tracking branch 'remotes/bantu/ticket/11538' into develop-olympus

* remotes/bantu/ticket/11538:
  [ticket/11538] Cut functional tests down a bit as these are more expensive.
  [ticket/11538] Compare to '' instead of using empty(), so '0' does not pass.
  [ticket/11538] Add unit tests for phpbb_validate_hex_colour().
[ticket/11575] Correct test_cross_join() to test_order_lower().

This test does not do any cross joining, it only tests ORDER BY LOWER(...).

PHPBB3-11575
[ticket/11576] MySQL unit tests: Enable STRICT_TRANS_TABLES and others.

PHPBB3-11576
Merge remote-tracking branch 'bantu/ticket/11575' into develop-olympus

* bantu/ticket/11575:
  [ticket/11575] Correct test_cross_join() to test_order_lower().
Merge remote-tracking branch 'bantu/ticket/11576' into develop-olympus

* bantu/ticket/11576:
  [ticket/11576] MySQL unit tests: Enable STRICT_TRANS_TABLES and others.