os: Add facilities for client ID tracking.

An interface is provided for figuring out the PID and process name of
a client. Make some existing functionality from SELinux and IA
extensions available for general use.

Signed-off-by: Rami Ylimäki <rami.ylimaki@vincit.fi>
Reviewed-by: Tiago Vignatti <tiago.vignatti@nokia.com>

include/dix-config.h.in

@@ -279,6 +279,9 @@
 /* Support X resource extension */
 #undef RES
 
+/* Support client ID tracking in X resource extension */
+#undef CLIENTIDS
+
 /* Support MIT-SCREEN-SAVER extension */
 #undef SCREENSAVER