add a Makefile switch to avoid gettext translation in shell scripts

add a Makefile switch to avoid gettext translation in shell scripts

Some systems have gettext.sh (GNU gettext) installed, but it is either
broken or misconfigured in such a way so its output is not usable.  In
case the users of these systems are unable or not interested in fixing
them, setting the new Makefile switch should help:

    make USE_GETTEXT_SCHEME=fallthrough

This will replace the translation routines with fallthrough versions,
that does not use gettext from the platform.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>