Add support for tight encoding [1]. This patch only add support
for "basic" tight compression without any filter.

[1] http://tigervnc.org/cgi-bin/rfbproto#tight-encoding

.

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