ReviewRequest.changeset_is_pending was broken when we did some changes

to the repository/scmtool API, because we neglected to replace the call

to get_scmtool(). This wasn't caught by our existing unit test because

the test was broken in a couple ways (it wasn't properly setting

supports_pending_changesets on the SCMTool class, and the check for

the new commit ID was overwriting the old value and then testing a

variable against itself).

Ran the fixed unit test and saw it fail. Applied the fix and saw all

unit tests succeed.