Patch for HttpMock to allow options that reduce strictness of request matching

Hi,

I submitted a patch to lighthouse which allows users of
ActiveResource::HttpMock to relax the strictness of the request
matching algorithm in cases when exact matching of path or request
headers is not required for the purposes of the test.

See the patch at: http://rails.lighthouseapp.com/attachments/89958/http_mock_mock_options.diff

And ticket: http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/2002-httpmock-often-too-strict-in-matching-requests

With this patch, it is much easier to specify mocks that will match
incoming requests which contain query-strings as part of the URL, or
multiple request headers, saving unnecessary coding effort.

If someone could take a look at this patch that would be great,

Thanks,

Michael