#47 cleanups.
· Test failed using Mercurial 2.6. Need to ensure there is at least one commit on the default branch, or hg says ‘abort: unknown revision 'default'!’
· Removing use of reflection. Package-private (default) access is appropriate for invoking methods from tests.
· Checking ChangeComparator immediately in #compare rather than doing possibly irrelevant work first.
· Do not extend SCMTestBase as this runs dozens of extra (inherited) tests and makes a build much longer. Just need to use MercurialRule directly.
· Sundry stylistic changes, Javadoc, fixed imports, etc.