Using the ActiveRecord validations is smart in order to lessen load on
the project to develop our own validators, but it's problematic in that
calling `valid?` on the record fires off all the other validations --
including those on fields which may not be set yet because of
mass-assignment. This commit will "pre-validate" the attachment's fields
so that it doesn't process an invalid attachment, but it does so by
running its validations manually on assignment.

This allows bundler to complete gem dependency resolution during
development. This is only relevant for paperclip developers. Please see:
https://github.com/thoughtbot/paperclip/issues/1256 and thanks to
@nkondratyev

* Fixed tests and functionality for new fog and removed the fixed version from the gemspec
* Set time to 3600 from the current time so expiring actually works

`aws-sdk` has been updated to support newer version of nokogiri, so we
should loosen our dependency.

Needs work for S3 Attachments.

This is necessary so Gemnesium will be green.

The original commit came from @amazonwebservices and @trevorrowe in #579.
I had to revise the commit and make sure all the test cases are passing.
All credits still goes to those guys, thanks a lot!

This also removes Pry.

This test will generate a basic Rails application, include Paperclip
into Gemfile, and call basic `has_attached_file` in the model. This will
make sure that we're not messing up any of the configuration and
integration for our gem and the Rails framework.

Closes #507

(cherry picked from commit e053805f55b872e6926dfbfa14f38d1296e8b922)