Changes required to support android.

The new android support uses GL2, so we need to change some defines
to use it.
Force use of shaders on android.

The auto-detect code fails on ES.
Merge branch 'master' into android
Improve OpenGL ES2 support.
Merge branch 'master' into android
Merge branch 'master' into android
Merge branch 'master' into android
Merge branch 'master' into android
Read assets from an expansion file if one is available on Android.