scope fix

This should be uniq not DISTINCT
Update mailbox_spec.rb
Merge pull request #253 from Musaffa/master

configuration options for maximum length of subject and body.
Merge pull request #250 from ahmadhussain/patch-1

scope fix
Exclude Rails 4.1 from the gemspec. It generates bad queries
Test with rails 4.0
Remove unsuported rails from test suite
Use latest stable for major rails versions in tests
Fix appraisals warnings

"Your Gemfile lists the gem mailboxer (>= 0) more than once"
Remove check for unsupported ruby
Bring rails 4.1 support
Merge pull request #254 from deivid-rodriguez/rails_4_1_support

Rails 4 1 support
Bump version to 0.12.0.rc1
is_feedback attribute to conversation