Modify GLES2 headers to reflect WebGL-supported features

This adds a small change to some of the defines in GLES2/gl2ext.h,
telling applications that float and half float textures are not supported
on this platform.
Add missing function prototypes to GLES2/gl2ext.h

This adds some prototypes for functions used by the Ogre GLES2 RenderSystem
to emscripten's gl2ext.h file. This is necessary for Ogre to compile.
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming
move emscripten_GetProcAddress to a C library, so that it is less hackish and can work in fastcomp
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming
move emscripten_GetProcAddress to a C library, so that it is less hackish and can work in fastcomp
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming

Conflicts:
	tools/system_libs.py
Update to incoming, because there was a conflict, for some reason
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming

Conflicts:
	src/library_gl.js
	system/lib/gl.c
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming
Merge branch 'incoming' of https://github.com/kripken/emscripten into incoming