[cairo] cairo_xlib_surface_create_for_pixmap ()

[Steve Chaplin]

The format argument for cairo_xlib_surface_create_for_pixmap () says
"format : a standard Cairo pixel data format. The depth (number of of bits
 used) for the format must match the depth of pixmap."

Why not use gdk_drawable_get_depth() to read the depth of of the pixmap 
and use it to set format, and remove the format argument? It would prevent
any depth mismatch errors.

Also, shouldn't the return value be
"Returns : the newly created surface or NULL"?

Steve