Update Django from v1.6.5 to v1.6.8

This update should be unproblematic and is included to have some security issues
and other bugs fixed.
Update PgMagick from v0.5.7 to v0.5.8

This fixes a compilation issue on Mac OS X and should be an unproblematic
update.
Update south from v0.8.4 to v1.0.1

South is the migration system we use at the moment (which will likely change
with Django 1.7). This update to South' last major relase should be
unproblematic and brings in mainly some fixes, better error messages and
preparation for a smoother transition to Django 1.7 based migrations.