[ticket/10772] Use forum specific style for trigger_error

PHPBB3-10772
[ticket/10772] Functional tests for forum style

PHPBB3-10772
[ticket/10772] Remove unnecessary comment

PHPBB3-10772
Merge remote-tracking branch 'remotes/cyberalien/ticket/10772' into develop-olympus

# By Vjacheslav Trushkin
# Via Vjacheslav Trushkin
* remotes/cyberalien/ticket/10772:
  [ticket/10772] Remove unnecessary comment
  [ticket/10772] Functional tests for forum style
  [ticket/10772] Use forum specific style for trigger_error