Added NME_GLES2 define, to begin to build full OpenGL ES 2.0 support

Unless we dynamically reference the OpenGL ES library, most mobile platforms do not make it possible to switch between GLES1 and GLES2 without specifying this at compile time, BlackBerry does make this possible.

You can use "nme rebuild <target> -DNME_GLES2" to specify GL ES 2 instead of 1.1 support. There need to be some improvements to OpenGLContext.cpp to work entirely from GLES 2, but this will send us in the right direction
Got Pirate Pig working with OpenGL ES 2