Makefile.in: fix patch-wrapper checks

293c4ddb added checks to Makefile.in to disable the patch-wrapper test
when the configure script is not invoked with the --with-patch-wrapper
argument.  Those checks assumed that PATCH_WRAPPER will always be empty
unless --with-patch-wrapper was used.  However, PATCH_WRAPPER will be
set to "no" when the configure script is invoked with the
--without-patch-wrapper argument.

Reported-by: Kent R. Spillner <kspillner@acm.org>
Signed-off-by: Andreas Gruenbacher <andreas.gruenbacher@gmail.com>
faildiff.test: loosen error string constraint

diff might be called by a different name if the configure script was
invoked with the --with-diff argument.  Make the permissions test in
faildiff.test match other names as well.

Signed-off-by: Kent R. Spillner <kspillner@acm.org>