Always use attributes for gles

I hope this is ok as my next branch/pull request will build on top of it.

I considered adding an option for this feature but since the specs ( http://www.khronos.org/files/opengles_shading_language.pdf ) directly state "There are no built-in attribute names in OpenGL ES", I decided against it. If this lack of option is a deal-breaker for you then no worries, I will add one, hopefully defaulting to enabled though :-)