[ticket/11386] Send list of migrations instead of using load_migrations

Remove dependency of extension manager for migrator.

Keeping load_migrations function for others to use if they desire
but requiring the finder be sent to it in order to use it.

PHPBB3-11386
[ticket/11386] Fix missing ;

PHPBB3-11386
Merge branch 'develop' of git://github.com/phpbb/phpbb3 into ticket/11386-3

Conflicts:
	phpBB/includes/db/migrator.php
Merge remote-tracking branch 'EXreaction/ticket/11386-3' into develop

# By Nathaniel Guse
# Via Nathaniel Guse
* EXreaction/ticket/11386-3:
  [ticket/11386] Fix missing ;
  [ticket/11386] Send list of migrations instead of using load_migrations