Add some RSpec / Test::Unit helpers for context verification and apply_to_user? tests

[ReneB]

It would be nice if Arrthorizer users could use a syntax like

SomeRole.should apply_to_user(user, context)

# or

expect(SomeRole).to apply_to_user(user, context)

and

# controller configuration test
controller.context_for(:some_action).should_match(hash_or_context)

# or

expect(controller.context_for(:some_action)).to match(hash_or_context)

with the right error messages and all.

[ReneB]

apply_to_user is done. Context-matcher still needs to be done.