SF bug #478949 Windows installer start menu registry.

I'm guessing at this, pending more info from the bug submitter.  Wise
changed how the %GROUP% vrbl got defined between versions 5.0a (used
before Python 2.2) and 8.14, to hold the full path to Start Menu group
instead of just the group name.  If I'm guessing correctly, the info
the bug report is complaining about is in one of the registry keys
we set up that neither Windows nor Python cares about.  We did store
a full path there in 2.2b1 instead of just the group name; the patch cuts
it back to just the name again.