add method to find the android ndk build executable in a common way for all sub projects that need to build a native android lib
reorganize build of Android OpenAL Soft lib
Merge commit 'a0ccd9984c328dda80df3acffad6095e76878c52'
Merge commit 'f5c841aac54c09cb038d942407245f440f1d02d6'
add native android lib for loading png and gif files.  Does not premultiply.  Uses stb_image (http://www.nothings.org/stb_image.c)
Change AndroidAssetManager to use the native lib to load png and gif files