Add ZRLE [1] and ZYWRLE [2] encodings. The code is inspire^W stolen
from libvncserver (again), but have been rewriten to match QEMU coding
style.

[1] http://www.realvnc.com/docs/rfbproto.pdf
[2] http://micro-vnc.jp/research/remote_desktop_ng/ZYWRLE/publications/



Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>