Log Message:
Update ruby-rspec-mocks to 2.13.0.

### 2.13.0 / 2013-02-23
[full changelog](http://github.com/rspec/rspec-mocks/compare/v2.12.2...v2.13.0)

Bug fixes

* Fix bug that caused weird behavior when a method that had
  previously been stubbed with multiple return values (e.g.
  `obj.stub(:foo).and_return(1, 2)`) was later mocked with a
  single return value (e.g. `obj.should_receive(:foo).once.and_return(1)`).
  (Myron Marston)
* Fix bug related to a mock expectation for a method that already had
  multiple stubs with different `with` constraints. Previously, the
  first stub was used, even though it may not have matched the passed
  args. The fix defers this decision until the message is received so
  that the proper stub response can be chosen based on the passed
  arguments (Myron Marston).
* Do not call `nil?` extra times on a mocked object, in case `nil?`
  itself is expected a set number of times (Myron Marston).
* Fix `missing_default_stub_error` message so array args are handled
  properly (Myron Marston).
* Explicitly disallow `any_instance.unstub!` (Ryan Jones).
* Fix `any_instance` stubbing so that it works with `Delegator`
  subclasses (Myron Marston).
* Fix `and_call_original` so that it works with `Delegator` subclasses
  (Myron Marston).
* Fix `any_instance.should_not_receive` when `any_instance.should_receive`
  is used on the same class in the same example. Previously it would
  wrongly report a failure even when the message was not received
  (Myron Marston).