requirements: Ensure we have latest South

South 1.0 will now only get security and bugfix updates, so lets just
forget about the versioning. 1.0 we need for any combined South and
Django migrations that could be needed.
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).
Syncing with core: Drop TMUnit

Probably it is not necessary to remove most of the other code, and
maybe even some of it is left behind, but since we just want to
sync our models with core it is not so important.