vnc dirty tracking optinizations.
various vnc bugfixes.

# gpg: Signature made Mon 10 Mar 2014 12:39:54 GMT using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"

* remotes/kraxel/tags/pull-vnc-1:
  ui/vnc: disable adaptive update calculations if not needed
  ui/vnc: optimize setting in vnc_dpy_update()
  ui/vnc: optimize clearing in find_and_clear_dirty_height()
  ui/vnc: optimize dirty bitmap tracking
  ui/vnc: derive cmp_bytes from VNC_DIRTY_PIXELS_PER_BIT
  ui/vnc: introduce VNC_DIRTY_PIXELS_PER_BIT macro
  vnc: fix use-after-free in vnc_update_client_sync
  vnc: Fix qemu crashed when vnc client disconnect suddenly
  vnc: Fix tight_detect_smooth_image() for lossless case

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>