fix InController for ruby 2.0's respond_to?

respond_to? returns false for protected methods in ruby 2.0, which is
used to test existence of new/load methods in controllers. This changes
those calls to respond_to?(..., true) which returns true for protected
(or private) methods.
Fix: use model.primary_key instead of :id
Avoid call to current_user in AuthorizationInController#permitted_to*
when :user option is passed.
Merge pull request #160 from jhawthorn/ruby2.0

support ruby-2.0.0-preview1
Merge pull request #166 from tovodeverett/avoid_current_user_call

Avoid call to current_user in AuthorizationInController#permitted_to* when :user option is passed.
Merge pull request #167 from lejoko/fix_primary_key

Fix: use model.primary_key instead of :id
Bumped minor to 0.5.7
Added Authorization.current_user_accessor as custom devise current_user helper