[cairo] ARGB surface for A8

[L A]

My hardware does not seem to like the A8 format. I have noticed that
clips and paths use this format in cairo. I was thinking of either
changing CAIRO_CONTENT_ALPHAs to CAIRO_CONTENT_COLOR_ALPHA or to
allocate ARGB surfaces when the pixel format is CAIRO_FORMAT_A8 and
set the surface pixman_format as ARGB. Do you see any problems with
these? If you do, can you offer alternatives?

Thanks
Levent