Fixed set_content_type for classes not responding to :content_type=

Changed from "set_instance_variable" to using
Object#instance_variable_set to make it work.
Merge pull request #556 from anoras/master

Fixed bug in MimeTypes integration when setting the content type through an instance variable.
add query options for s3 to support response headers overwriting
Allow conditionals to accept blocks
Merge pull request #567 from chrisroberts/master

Allow conditionals to accept blocks
Remove false assignment from testing. Set to file instance.
Use https rubygems source
Merge pull request #568 from chrisroberts/master

Assign :file to file instance when calling blocks
Merge pull request #566 from autohaus24/add_query_options_for_s3_to_support_response_headers_overwriting

add query options for s3 to support response headers overwriting
Fix possible race condition with CarrierWave.root, closes #544
Only test against one rbx, there is only one
Fixing the README to show the right way to get the identifier for a specific uploaded file
Merge pull request #569 from rubemz/master

Fixing the README to show properly how to get an identifier for an uploaded file
With Active Record ORM, setting remote_url marks mounted column as dirty, closes #512
clean up gemspec deps, make sure we use latest cucumber on travis
Re: 98a5a7, clarify test name
Drop support for rbx on Travis for now, too unstable
Run travis against Rails 3-0-stable, 3-1-stable, 3-2-stable
Test rails master as well, but exclude 1.8.7 and ree since rails 4 requires 1.9.3
Support rails beyond 3.x