src/wav.c : Handle 'smpl' chunks with loop count of 0.

Closes: https://github.com/erikd/libsndfile/issues/86
src/Makefile.am : Update CLEANFILES.
configure.ac : Add detection of -fsanitizer=undefined.

Both Clang and GCC-4.9 now support the undefined behaviour sanitizer
so detect and enable it when configuring with --enable-sanitizer.

Also improve configure reporting of sanitizer and stack smash
protection.
src/ : Fix undefined behaviour warnings.
tests/ : Fix undefined behaviour warnings.