tests: fail if gf_methods is not found

If the gf_methods was not found, the test would silently succeed doing
nothing. Check for existence and fail if it is not in the path.

Signed-off-by: Loic Dachary <loic@dachary.org>

Examples/test_all_gfs.sh

@@ -1,4 +1,4 @@
-#
+#!/bin/bash
 #
 # Copyright (c) 2013, James S. Plank and Kevin Greenan
 # All rights reserved.
@@ -42,6 +42,11 @@ k=12
 m=3
 seed=1370
 
+if ! test -x ${GF_METHODS} ; then
+    ${GF_METHODS}
+    exit 1
+fi
+
 # Test all w=8
 ${GF_METHODS} 8 -B -L | awk -F: '{ if ($1 == "w=8") print $2; }' |
 while read method; do