Inherit method security

Closes #415
Only check security if it is already set
Reorganise test integration

Adds compatibility with minitest-rails 0.5
Enable testing against multiple Rails versions
Rails 3.0 compatibility
Rails 3.1 compatibility
Update development dependencies

Add rspec-rails, remove yard, and allow rake 10.0+
Merge pull request #416 from haines/inherit_security

Inherit method security and test against Rails 3.x
Pretend to be instance_of?(source.class)
Remove pending spec on Rails 3.0
Merge pull request #417 from haines/instance_of

Pretend to be instance_of?(source.class)