Fix issues with 'make test-tarball' with --disable-shared.

When shared libs are disabled the binaries end up in a .libs/
dir while when they're enabled there is no .libs/ dir.
doc/donate.html : Replace Paypal donation with Butcoin.
src/common.[ch] : Add function psf_open_tmpfile.
src/alac.c : Fix bug on android due to failing tmp file.

The ALAC encoder was attempting to open a temporary file in /tmp
which does not exist on Android and this wasn't being caught.
The solution was to try and open the temp file in the current
directory if /tmp does not exist.

Closes: https://github.com/erikd/libsndfile/issues/46
Configure improvements for Android.
configure.ac : CFLAGS and CXXFLAGS tweaks.