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>
examples/*/Makefile.am : Add CLEANFILES line to remove Windows .exe files.
src/libFLAC/stream_decoder.c : Fail safely to avoid a heap overflow.

This fix is closely related to the fix for CVE-2014-9028. When that
fix went public Miroslav Lichvar noticed a similar potential problem
spot in the same function and was able to craft a file to trigger a
heap write overflow.

Reported-by : Miroslav Lichvar <mlichvar@redhat.com>
Scripts/cross-build-win-binaries.mk : Add a 'clean' target.
Version 1.3.1 final.