Rewrite:

• Try not to hardcode anything. Intoduce a $subtrees variable which lists the CVS subtrees that need to be updated.
• Document all major variables and actions.
• Allow customization via the current environment (add some variables which can be set to facilitate testing and running outside of freefall).
• Do a fresh checkout of the sources every Sunday; previously this was only a make clean; a fresh checkout makes sure occasional CVS bogons don't mess anything up (requested by nik).
• Make $LOGFILE an absolute path so we don't end up with multiple log files, each containing half of the story.

Approved by: nik