git-cvsserver used checkout-index internally for commit and annotate.
Since a work tree is required for this to function now, this was
breaking. Work around this by defining GIT_WORK_TREE=. in the
appropriate places.
Signed-off-by: Brian Downing <bdowning@lavos.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>