Update to gnome-control-center 3.6 git as of today

This is a candidate for a version update but no bump is yet applied

* configure.in.in: now requires x11
* src/cut-n-paste/: update code from gnome-control-center
* src/{control-center.c, gnome-control-center.c, shell.ui}: rebase on updated code
* src/patch/: update patch to current changes