(clutter_stage_egl_realize): Use ES 2 renderable type when
building for GLES 2.
* clutter/eglnative/clutter-event-egl.c (get_backend_time): Added
a NULL for the microseconds parameter of g_timer_elapsed.
* clutter/eglnative/clutter-stage-egl.h:
* clutter/eglnative/clutter-egl.h:
* clutter/eglnative/clutter-backend-egl.h: Include
clutter-egl-headers.h instead of including the GL headers directly
so it can include gl2.h when building for GLES 2.
* clutter/eglnative/clutter-egl-headers.h:
* clutter/eglnative/Makefile.am (libclutter_eglnative_la_SOURCES):
Added clutter-egl-headers.h
* clutter/cogl/gles/cogl-fixed-fragment-shader.glsl: GLES 2
doesn't provide a default precision for floats in the fragment
shader and it will reject the shader if there isn't one.
