Extension can't be acivated if migration files are not in the order of dependency

If migration files (and classes) names (a-z) order are differ from it dependency, and the function depends_on() in migration files gives arrays with members does not start with a backslash (),
the extension activate will fail and you may got time exceded error.

for example:
the extension have these migration files/classes in order of dependency:
release_1_0
release_1_2
update_user_table
release_1_3

note that (update_user_table) come after (release_1_3) in a-z order, so the extension activate will fail unless the depends_on() function return names started with backslash. this error does not occur in phpBB 3.1.x and the extension activted normally but in phpBB 3.1.x the migration table have two rows for every migration one started with backslash and other not.