git-reset is yet another working tree manipulator, which should
be taught about submodules.
When a user uses git-reset and requests to recurse into submodules,
this will reset the submodules to the object name as recorded in the
superproject, detaching the HEADs.
Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>