[Xcb] low-level API changes

[Vincent Torri]

>
> Could you also do me a favor and recast your visibility patch, and any
> others I haven't committed, against the current code? There have been
> cleanups in configure.ac and all over that may make your patches
> cleaner.

hey,

i've already sent the patch for the visibility feature, but you don't
commit it, and you change xcbint.h (which is modified in my patch)...

Vincent