allows X drivers to add writeback entries as it converts
MTRR layout from continuous to discrete
details on 95ffa2438d0e9c48779f0106b1c0eb36165e759c
can be disabled with disable_mtrr_cleanup on bootup if crashes.
enabled in fedora too, let's see how it shakes here.
svn path=/dists/trunk/linux-2.6/; revision=12219