Simplify and speed up the process of finding the git worktree when
running on Windows by keeping it in perl and avoiding spawning helper
processes.
Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>