[Xcb] Callback based event handling

[Michael Stapelberg]

Hi Erik,

Excerpts from Erik Karlsson's message of 2012-02-23 10:51:37 +0100:
> The commit message discourages use of this library, and I then wonder, 
> what is the preferred method of handling XCB events?
The preferred way is to do this yourself — it’s rather easy. See
http://code.stapelberg.de/git/i3lock/tree/i3lock.c#n450 for an example.

Best regards,
Michael