[Cairo] Text APIs round 2

[Keith Packard]

Around 13 o'clock on Aug 15, Carl Worth wrote:

> (though in that case I was planning on having cairo_image_surface/
> cairo_x11_surface/etc. all return pointers to objects of the same type:
> cairo_surface_t).

Perhaps we should give up on the small amount of type-safety that multiple 
pointer types provide and just use cairo_font_t for all of them.  That 
would eliminate several functions (which is always good).

-keith