Many tests didn't change back from subdirectories at the end of the tests ...
and they don't have to. The missing 'cd ..' could always be added when another
test case is added to the test file.
This change do that tests (99.5%) consistently end up in $TESTDIR where they
started, thus making it simpler to extend them or move them around.
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.
