use xstrncmpz()

Add and apply a semantic patch for calling xstrncmpz() to compare a
NUL-terminated string with a buffer of a known length instead of using
strncmp() and checking the terminating NUL explicitly.  This simplifies
callers by reducing code duplication.

I had to adjust remote.c manually because Coccinelle inexplicably
changed the indent of the else branches.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

archive-tar.c

@@ -365,7 +365,7 @@ static struct archiver *find_tar_filter(const char *name, size_t len)
 	int i;
 	for (i = 0; i < nr_tar_filters; i++) {
 		struct archiver *ar = tar_filters[i];
-		if (!strncmp(ar->name, name, len) && !ar->name[len])
+		if (!xstrncmpz(ar->name, name, len))
 			return ar;
 	}
 	return NULL;