add CHOST, PORTDIR, DISTDIR and PKGDIR to make.conf. Sync USE flags
remove xscreensaver from xfce4-session
don't compile git with webdav, python and gtk
use kernel 3.12.x instead of latest 3.13 until nouveau EFI VGA conflict is fixed

https://bugzilla.redhat.com/show_bug.cgi?id=1044304