Moved AR include into a configure method to prevent non-inclusion when using the git repo in the Gemfile

Rails.root returns a Pathname and you can now declare your attachment
without having to call #to_s first:

has_attached_file :avatar,
                  :storage => :s3,
                  :s3_credentials => Rails.root.join('s3.yml')
(cherry picked from commit 65d7600b7246cb3bd8f10805fb618e5839694318)

Added a rake task for testing all versions. Changed gem statements to use ~> instead of hard versions.

These callbacks are different from pre-rails 3. They do NOT cancel the
after_ if the before_ returns false. They will cancell inner callbacks,
however, but that's it. This is a change in functionality.

Determine content_type with file command's --mime-type when content_type is not found in the default cases.
(cherry picked from commit 2ca52df1)

styles encapsulated, to delay calling of procs until context is useful and to allow per-style processor lists

(cherry picked from commit 61dbcb3e36c0bc9742d045dd1e54f846043a1569)

Fixed an error where ImageMagick wasn't identifying images because the Tempfiles did not have the right extension.

(cherry picked from commit f58f73210621261c214136eb7514be459032ee0f)

(cherry picked from commit 43946120a6231be06d59c8f28969946c213e6872)