clutter-cairo-texture: Use the new cogl_pixel_buffer API

clutter-cairo-texture: Use the new cogl_pixel_buffer API

ClutterCairoTexture now stores the surface image data in a Cogl pixel
buffer object. When clutter_cairo_texture_create is called the buffer
is mapped and a new Cairo surface is created to render directly to the
PBO. When the surface is destroyed the buffer is unmapped and a Cogl
texture is recreated from the buffer. This should enable slightly
faster uploads when using Cairo because it avoids having to copy the
surface data to the texture.

http://bugzilla.openedhand.com/show_bug.cgi?id=1982

Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>