tests/*.sh : Switch back to /bin/sh.

Jan Stary reported that on OpenBSD bash isn't located in /bin/
which means that the test fail. He also noted that there didn't
seem to be anything bash specific in the tests.

This patch takes some suggestions from Jan, plus a few fixes tested
on Debian using the bin/sh provided by bash and dash.

Suggested-by: Jan Stary <hans@stare.cz>

test/test_bins.sh

@@ -1,4 +1,4 @@
-#!/bin/bash -e
+#!/bin/sh -e
 
 #  FLAC - Free Lossless Audio Codec
 #  Copyright (C) 2001-2009  Josh Coalson
@@ -18,7 +18,7 @@
 #  restrictive of those mentioned above.  See the file COPYING.Xiph in this
 #  distribution.
 
-source common.sh
+. ./common.sh
 
 PATH=../src/flac:$PATH
 PATH=../objs/$BUILD/bin:$PATH