Add automated filesystem checking based on scripts I've used now for

quite some time locally. Most of the test require root so they are
	skipped when run without necessarry privelegies.

tests/tar_test.in

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+set -e
+
+if ! which tar >/dev/null 2>&1; then
+   echo "tar not installed; cannot test tar."
+   exit 77
+fi
+
+"@builddir@/grub-fs-tester" tarfs