CFT update day 2

The highlights for today are the following:

Bug fixes:
- Will Andrews fixed attach for some laptops (such as the Carbon X1).
  The Carbon X1 has a quirky BIOS that doesn't allow the OS to
  enumerate the GPU's interrupt.
- Will Andrews identified a conditionally uninitialized return in
  idr_find that could lead to a panic in some cases.
- Fixed a panic in mtrr_del frequently seen when attach failed.
- Sleep/wakeups with interrupts are largely implemented correctly
  now. Previously a polling 10ms sleep was used. I'm still
  concerned that the code really needs to be level-triggered.

Cleanups:
- Logging is now enabled for the first 10s after attach unless
  dev.drm.drm_debug_keep=1.
- Unimplemented warnings are off by default.

As of this moment the latest USB image is:
 http://www.bsddesktop.com/images/cftdisk_2016052307.img.xz

The USB image now has sync disabled on var. This should improve
responsiveness for most people with slow USB pen drives. If
you're having issues that require retaining logs you'll need
to "zfs set sync=enabled zrootusb/var".

The USB image now includes kde4 and xfce. It is also much larger, for 
this iteration you will need a 16GB USB key. The next one will probably
not be quite so large. If size is a common problem let me know. It's 
difficult to buy a USB key that is less than 16GB today.

joeuser's .xinitrc is configured to start xfce with  startx. To start kde 
run: service kdm4 onestart.

Note that the image name has changed. The most recent should be
self-evident in: http://www.bsddesktop.com/images 

Helpful hint: use a 1MB blocksize for dd and run gpart recover
to fix label warnings. Assuming your USB pen drive shows up as
/dev/da0 and cftdisk image is the one I just posted:

unxz -f cftdisk_2016052307.img.xz; dd if=cftdisk_2016052307.img of=/dev/da0 bs=1M; gpart recover da0

And as a reminder, if you're having problems with X on the USB
key, try disabling it by moving /etc/X11/xorg.conf.d/20-intel.conf
somewhere else on your file system.

If using the github repo, make sure you're using the drm-next-4.6
branch.

Cheers.

-M