cvsimport: modernize callouts to git subcommands

cvsimport: modernize callouts to git subcommands

This patch updates all calling conventions for external git tools.  to
use the modern calling convention (eg: git foo instead of git-foo).
This is almost entierly a s/git-/git / operation, with deviations only
as required to keep tests passing.

Reported-by: Alexander Maier <amaier@opencsw.org>
Signed-off-by: Ben Walton <bwalton@artsci.utoronto.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>