add explicit kwargs to authenticate

Added explicit kwargs to `authenticate` so that if e.g. username and password are given to Django's main authenticate, Django detects that they will not work for this backend and skips it.
Merge pull request #490 from donaldharvey/master

add explicit kwargs to FacebookBackend.authenticate
bump and pep8
support last 2 versions of django in test flow
fixed versions
probably this is why south doesnt install properly
3.4.1
Delete __init__.py
removed south for 1.7
commit
Moved south migration folders to south_migration folder per
recommendation by south:
http://south.readthedocs.org/en/latest/releasenotes/1.0.html#library-migration-path

Fixes django 1.7 tests.
Settings doc update and ignore test images.  Django and python version
bumps.
looks like travis doesn't have python 3.4.2 yet...
pep8 fixes
print fix.
Fix pep8 to not look at south_migrations.
Merge pull request #497 from troygrosfield/master

Get tests successfully running for python 3.4 and django 1.7
Merge remote-tracking branch 'upstream/master'