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
Merge branch 'master' of github.com:haxenme/NME
Enabling OpenGL ES 2 shader support by default

If you need to use OpenGL ES 1, you must recompile the NME native binary using -DNME_FORCE_GLES1. Perhaps, it would be possible to automatically roll back to OpenGL ES 1 by dynamically loading the GL library, but for now the binary is hard-coded to compile against GLES2 (default) or GLES1 using the above flag.