Add some tight awareness to vnc.c (Alexander Graf)

Add some tight awareness to vnc.c (Alexander Graf)

This patch enables the vnc server to understand fundamental tight extensions.
It changes from a "Hextile or not" scheme when sending framebuffer updates to
a "preferred encoding", namely the last one set.

While this is not perfect, as actually a list of "preferred encodings" should
be kept, it's good enough for now.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6496 c046a42c-6fe2-441c-8c8c-71466251a162