[ticket/12415] Use private message instead of "pm" accronym

https://tracker.phpbb.com/browse/PHPBB3-12415

PHPBB3-12415
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12499] Incorrect call to phpbb\log\log::add() in db:migrate
Merge remote-tracking branch 'MGaetan89/ticket/12415' into develop-ascraeus

* MGaetan89/ticket/12415:
  [ticket/12415] Use private message instead of "pm" accronym
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12415] Use private message instead of "pm" accronym
Merge pull request #2409 from prototech/ticket/12491

[ticket/12491] Fix clashing USERNAME_FULL template variable.

* prototech/ticket/12491:
  [ticket/12491] Fix clashing USERNAME_FULL template variable.
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12491] Fix clashing USERNAME_FULL template variable.