Testing was done with a simple GNOME 2.28 session with a number of
applications open (gnome-terminal, VirtualBox, Firefox).

Primary test case was xwininfo -root -all, which listed 114 children of
the root window.   Output was identical to Xlib version (after applying
the fix to libxcb_icccm for always null-terminating wm_class properties).

Over a local connection on the same machine:

Xlib:	0.00u 0.01s 0:00.05 20.0%
xcb:	0.00u 0.00s 0:00.02 0.0%

(i.e. barely measurable difference - I had more variation between
 repeated runs of the command)

Introducing latency by running over ssh -X from California to Beijing
and back:

Xlib:	0.03u 0.02s 8:19.12 0.0%
xcb:	0.00u 0.00s 0:45.26 0.0%

Memory size when exit() is called:

Xlib:
 Address  Kbytes     RSS    Anon  Locked Mode   Mapped File
08043000      20      20      20       - rw---    [ stack ]
08400000     144     144     144       - rw---    [ heap ]
total Kb    8972    8640     316       -

xcb:
 Address  Kbytes     RSS    Anon  Locked Mode   Mapped File
08045000      12      12      12       - rwx--    [ stack ]
0806C000     100     100     100       - rwx--    [ heap ]
total Kb    7980    7692     288       -

Bytes sent & received (counted by proxying via xscope):

Xlib: Client --> Server: 21380 bytes   Client <-- Server:  54124 bytes
xcb:  Client --> Server: 21114 bytes   Client <-- Server:  53160 bytes

(The Xlib code didn't save any replies, so re-requested a couple of things
 when running with -all - I fixed that while porting to xcb, but the same
 could be done with Xlib easily too.)

Not yet handled: WM_NAME properties that need to be converted from another
character encoding.

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: James Cloos <cloos@jhcloos.com>