[prep-release-3.0.12] Bumping version number for 3.0.12-RC3.
[prep-release-3.0.12] Update Changelog for 3.0.12-RC3 release.
Merge branch 'prep-release-3.0.12' into develop-olympus

* prep-release-3.0.12:
  [prep-release-3.0.12] Update Changelog for 3.0.12-RC3 release.
  [prep-release-3.0.12] Bumping version number for 3.0.12-RC3.

Conflicts:
	phpBB/includes/constants.php
	phpBB/install/database_update.php
	phpBB/install/schemas/schema_data.sql