[ticket/11331] Inform user that double dots will be stripped from avatar paths

PHPBB3-11331
[ticket/12673] IMAGETYPE_SWC might be missing when SWC is not supported.

PHPBB3-12673
Merge remote-tracking branch 'bantu/ticket/12673' into develop-ascraeus

* bantu/ticket/12673:
  [ticket/12673] IMAGETYPE_SWC might be missing when SWC is not supported.
[ticket/12675] Fix code sniffer complaints introduced by recent commits

PHPBB3-12675
Merge pull request #2555 from marc1706/ticket/11331

[ticket/11331] Inform user that double dots will be stripped from avatar paths
Merge pull request #2561 from marc1706/ticket/12675

[ticket/12675] Fix code sniffer complaints introduced by recent commits

* marc1706/ticket/12675:
  [ticket/12675] Fix code sniffer complaints introduced by recent commits