Fixed tests + fixture for issue2635

- Bug fix for issue 2635 is broken down into 2 parts
- Part 1 of this fix is made in resources.py in an earlier commit
- Part 2 of this fix is made in the current commit: affected files are
  - reviewboard/reviews/fixtures/test_reviewrequests.json
  - reviewboard/webapi/tests.py
- Had run into a strange error: "DoesNotExist: LocalSite matching query
  does not exist.", which was solved by decorating the ship_it tests
  with @add_fixtures(['test_site'])
- In test_reviewrequests.json, corrected the shipit_count of a
  review-request with pk=2 from 0 to 1, as there is a review associated
  with that review-request with ship-it set to True

Merge branch 'release-1.6.x' into issue2635-slchen


Merge branch 'release-1.6.x' into issue2635-slchen


Fixed Issue: 2635 - "shipit=0" issue

- (release.1.6.x)
- see http://code.google.com/p/reviewboard/issues/detail?id=2635 for
  full details
- replaced (removed) exclude_q infrastructure for filtering
  review-requests based on ship-out counts
- instead uses existing q infrastructure for filtering (similar to how
  it is used for the other search parameters); fixed the filtering
  parameter for requests from "reviews__shipit" to "shipit_count"

Manual testing on local environment for release.1.6.x