The default keyed_surface is meant to handle CoglTextures thus we can't
add cairo surfaces to it, as the DestroyNotify function won't handle them.
Then the quicker way is to just add another Hash table for handling
such types of textures, with proper destroy function.
(cherry picked from commit 1f03599d1cf888f73a33363212b99905064e2c9e)
4b2e0247af