-Add: Django 1.7 support.

Note, not all is tested, but this should be enough to work without
following the entire refractor tree.
-Add: has_results support.

.exists now calls .has_results() ,as such, we process results_iter() and
return if there is at least one item. (We thern do not process the rest
of the items).
-Add: allow_migrate for the Router

1.7 now calls allow_migrate instead of allow_syncdb ; since we do not
want to create a LDAP database, we return False...
Merge pull request #33 from Xaroth/django-1.7-support

Add Django 1.7 support.