Added a rails_master section to Gemfile
No more `with_default_scope` on Rails master, see https://github.com/rails/rails/commit/94924dc32baf78f13e289172534c2e71c9c8cade
Added a reload to fix a test broken on master

I am not sure why this is wokring on Rails 4, but the problem is that `post3`
here is holding on to an old reference of some associations so `PostDestroyer`
is not doing the right thing.
Merge pull request #1709 from chancancode/boot_to_master

Make Discourse work on Rails master (4.1)