Remove the PATH_MAX limitation from the environment setting that
points to a filename by switching to dynamic allocation.
As a side effect of this change, we also reduce the snprintf()
calls, that may silently truncate results if the programmer is not
careful.
Helped-by: Junio C Hamano <gitster@pobox.com> Helped-by: Jeff King <peff@peff.net> Signed-off-by: Elia Pinto <gitter.spiros@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>