MFC r273796

Import in latest mtree from NetBSD to fix a bug in parsing group files
that jmg fixed upstream.

Sponsored by:	DARPA, AFRL
MFC r274095:
  Fix VOLUME_LABEL when BRANCH contains '-' and '.'
  characters, in particular '-' and '.'.

Insta-MFC ok:	re (hrs)
Sponsored by:	The FreeBSD Foundation