Spec for deprecaton call site

This is actually what started all my `CallerFilter` changes tonight:

* I was in rspec-mocks, backporting Jon's recent PR to the 2-99-maintenance branch.
* We haven't updated it for the latest deprecation warnings (we still should), including `be_false`, and I noticed that the call site printed for that was in `rspec/matchers.rb` -- which is wrong.
* I traced it down to this line in rspec-core's `deprecate`:

``` ruby
call_site = caller.find { |line| line !~ %r{/lib/rspec/(core|mocks|expectations|matchers|rails)/} }
```

The problem is that this will grab a line like `rspec/core.rb` or `rspec/matchers.rb`.  I realized that it's fixed in the `CallerFilter` thing so figured it was time to make that consistent everywhere :).

Anyhow, this'll fail until rspec-core's PR is merged (I plan to merge it tomorrow), but I wanted to open this and add the spec before I forgot.