git-submodule - allow a relative path as the subproject url

git-submodule - allow a relative path as the subproject url

This allows a subproject's location to be specified and stored as relative
to the parent project's location (e.g., ./foo, or ../foo). This url is
stored in .gitmodules as given. It is resolved into an absolute url by
appending it to the parent project's url when the information is written
to .git/config (i.e., during submodule add for the originator, and
submodule init for a downstream recipient). This allows cloning of the
project to work "as expected" if the project is hosted on a different
server than when the subprojects were added.

Signed-off-by: Mark Levedahl <mdl123@verizon.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>