Without specifying the parent revision of the working copy, users will
update to tip, which is most likely the other head they were trying to
merge, not the revision they were at before the merge.
Many tests fixed the commit date of their changesets at '1000000 0' or
similar. However testing with "Mon Jan 12 13:46:40 1970 +0000" is not
better than testing with "Thu Jan 01 00:00:00 1970 +0000", which is
the default run-tests.py installs.
Removing the unnecessary flag removes some clutter and will hopefully
make it clearer what the tests are really trying to test. Some tests
did not even change their output when the dates were changed, in which
case the -d flag was truly irrelevant.
Dates used in sequence (such as '0 0', '1 0', etc...) were left alone
since they may make the test easier to understand.
