Allow ls-files to recognize submodules in order to retrieve a list of
files from a repository's submodules.  This is done by forking off a
process to recursively call ls-files on all submodules. Use top-level
--super-prefix option to pass a path to the submodule which it can
use to prepend to output or pathspec matching logic.
Signed-off-by: NBrandon Williams <bmwill@google.com>
Reviewed-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>