Add Retina support to filer when using easy thumbnails
more prominently show that PIL needs JPEG support
PEP8 cleanup
Changed function signature get_thumbnail_name to be compatible with easy_thumbnails supporting hires images
Update filer/admin/permissionadmin.py

Added some admin options to the folder permissions to improve usability.
Update filer/models/imagemodels.py

Removed checking for staff user when serving images 
with permissions through filer. This should be like it is 
with regular files and folders.
Merge pull request #300 from zombat/develop

Improve usability in Permission Admin and fixed download permission issue
Merge pull request #299 from jrief/retina-display

Add Retina support to filer when using easy thumbnails