git-cvsserver: no longer use deprecated 'git-subcommand' commands

git-cvsserver still references git commands like 'git-config', which
is depcrecated.  This commit changes git-cvsserver to use the
'git subcommand' form.

Sylvain Beucler reported the problem through
 http://bugs.debian.org/536067

Signed-off-by: Gerrit Pape <pape@smarden.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>