bin/tahoe @python should always invoke the same Python that ran bin/tahoe.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>
Update CREDITS.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>
Delete the obsolete misc/build_helpers/test_mac_diskimage.py script.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>