Submodules: Add the "fetchRecurseSubmodules" config option

Submodules: Add the "fetchRecurseSubmodules" config option

The new boolean "fetchRecurseSubmodules" config option controls the
behavior for "git fetch" and "git pull". It specifies if these commands
should recurse into submodules and fetch new commits there too and can be
set separately for each submodule.

In the .gitmodules file "submodule.<name>.fetchRecurseSubmodules" entries
are read before looking for them in .git/config. Thus settings found in
.git/config will override those from .gitmodules, thereby allowing the
user to ignore settings given by the remote side while also letting
upstream set reasonable defaults for those users who don't have special
needs.

This configuration can be overridden by the command line option
"--[no-]recurse-submodules" of "git fetch" and "git pull".

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>