Django 1.6: renamed `get_query_set()` to `get_queryset()`

Fixes evernote/pootle#181.
Followup for Django 1.6: renamed `get_query_set()` to `get_queryset()`
More changes to reduce diff
Reduce diff: Don't prefix with log
Syncing with core: Add obsolete field in Directory
Syncing with core: Remove translation_project field in Suggestion
Syncing with core: Remove uniqueness constraint in Suggestion

Allows to submit suggestions that have already been (maybe accidentally)
rejected.

Note that the `auto_now_add=True` of suggestion's `creation_time` field
has been adapted too. South was somehow setting this to `NULL` and this
avoids that weird behavior.

Pick note: picked from evernote/pootle@67e9a408 (only model changes,
the migration has been recreated).