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

### 2.13.0 / 2013-02-23
[full \ 
changelog](http://github.com/rspec/rspec-expectations/compare/v2.12.1...v2.13.0)

Enhancements

* Add support for percent deltas to `be_within` matcher:
  `expect(value).to be_within(10).percent_of(expected)`
  (Myron Marston).
* Add support to `include` matcher to allow it to be given a list
  of matchers as the expecteds to match against (Luke Redpath).

Bug fixes

* Fix `change` matcher so that it dups strings in order to handle
  mutated strings (Myron Marston).
* Fix `should be =~ /some regex/` / `expect(...).to be =~ /some regex/`.
  Previously, these either failed with a confusing `undefined method
  matches?' for false:FalseClass` error or were no-ops that didn't
  actually verify anything (Myron Marston).
* Add compatibility for diff-lcs 1.2 and relax the version
  constraint (Peter Goldstein).
* Fix DSL-generated matchers to allow multiple instances of the
  same matcher in the same example to have different description
  and failure messages based on the expected value (Myron Marston).
* Prevent `undefined method #split for Array` error when dumping
  the diff of an array of multiline strings (Myron Marston).
* Don't blow up when comparing strings that are in an encoding
  that is not ASCII compatible (Myron Marston).
* Remove confusing "Check the implementation of #==" message
  printed for empty diffs (Myron Marston).