Code review comment for lp:~compiz-team/compiz/compiz.gles2.always-swapbuffers.1

Hi, resubmitted with the following changes:

1. Got the fallback logic under test, created an abstraction that we could use for both EGL and GLX, which removed some ifdef soup
2. Called SwapBuffers if fullscreen damage or painting to FBO
3. Added startup requirement on GLX_MESA_copy_sub_buffer / EGL_NV_post_sub_buffer OR GLX_EXT_framebuffer_object OR OpenGL ES 2.0
4. Removed EGL_BUFFER_PRESERVED call in eglSurfaceAttrib, we no longer need to do this as the framebuffer object is our main output device (incidentally , this should provide a small speed boost as there is no longer an implicit glReadPixels / glDrawPixels done inside of eglSwapBuffers : see http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html)