Fix require for class_attribute
Cheaper attribute_method_matchers

Conflicts:
	activemodel/lib/active_model/attribute_methods.rb
Fewer object allocations

Conflicts:
	activemodel/lib/active_model/attribute_methods.rb
allocate less objects
don't bother checking for respond_to? here
Merge pull request #65 from github/3-0-github+faster-attr-lookup

[3.0] Faster attr lookup