Add a configure flag for disabling soname versions

The loader on Android cannot deal with soname versions properly. To circumvent this problem, libtool has a -avoid-version flag that does not versionate the shared libraries.

To disable soname versions, "./configure --disable-soname". Soname versions are enabled by default, as only Android needs to disable them
Merge pull request #751 from sonOfRa/master

Add a configure flag for disabling soname versions