Prefix BLOG_USE_FEATURED_IMAGE in blog templates with settings., otherwise it always evalutes to False.

--HG--
branch : bugfix
Merged in joshcartme/mezzanine/bugfix (pull request #37)

Prefix BLOG_USE_FEATURED_IMAGE in blog templates with settings.
Fix site permissions lookup for non-superusers in admin sites drop-down.
Merge
Bump version to 1.4.1
Added tag 1.4.1 for changeset 422325d0533c
Updated changelog, requirements
Added ratings to comments, with new settings COMMENTS_USE_RATINGS for toggle ratings form in comments, and RATINGS_RANGE for defining valid ratings, replacing the old min/max settings. Also added _sum field injections for models with rating fields, and rating_date field on ratings, for use with time scaled scores.
Ensure emails are lowercased for gravatar hashes.
Fix page tree admin template when reversion is used.
Added new site to README.
Enhanced args to gravatar URLs.
Added Jesus Armando Anaya Orozco to AUTHORS.
Bump version to 1.4.2
Added tag 1.4.2 for changeset 2e2316c77d8d
Update automated changelog, settings docs, model graphs.