clone: Add the --recurse-submodules option as alias for --recursive

clone: Add the --recurse-submodules option as alias for --recursive

Since 1.6.5 "git clone" honors the --recursive option to recursively check
out submodules too. As this option can easily be misinterpreted when it is
added to other commands like "git grep", add the new --recurse-submodules
option as an alias for --recursive so the same option can be used for all
commands recursing into submodules.

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