xextproto and libXext cleanup

[Peter Hutterer]

Those of you watching xorg-announce or xorg-commit may have noticed that I
pushed the changes to xextproto and libXext.

This commit series removed all client-side headers from xextproto and moved
them into libXext instead. Clients should not be affected by this other than
that the BuildRequires have changed.

Most video drivers were affected (dpms.h -> dpmsconst.h). The patches for
intel and radeonhd are in Keith's + Eric and Matthias inboxes. I've
pushed updates for the rest of the video drivers myself.

The rule for header files are now:
Xfoo.h - library header file in libXext
foo.h - extension constants, xextproto
fooproto.h - protocol structures, xextproto

for those headers where foo.h was already in use as client-side header (e.g.
sync.h, dpms.h) the naming is
foo.h - library header in libXext
fooconst.h - extension constants, xextproto
fooproto.h - protocol structures, xextproto

If there are any build errors, please let me know. I'll be monitoring
tinderbox for the next few hours.

Cheers,
  Peter