GFileMonitor: Add kqueue(3) support to GIO

Written by Dmitry Matveev as part of GSoC 2011:
http://netbsd-soc.sourceforge.net/projects/kqueue4gio/

This brings native file monitoring support on systems supporting kqueue(3)
(all BSDs) and remove the need to rely on the unmaintained gamin software.
The backend adds GKqueueDirectoryMonitor and GKqueueFileMonitor.

Some parts rewritten by myself (to prevent needing a configuration file).
Helpful inputs from Colin Walters and Simon McVittie.

https://bugzilla.gnome.org/show_bug.cgi?id=679793