We now filter incoming data, which means we can start assuming the
clipboard data is always null terminated. This allows us to clean
up a lot of the internal handling.

This is required by the protocol so we should make sure it is
enforced. We are tolerant of clients that violate this though and
convert incoming clipboard data.

The normal Xorg server doesn't check this field, so neither can we
as there are applications relying on this leniancy.

ChangeWindowProperty() was removed upstream because it was redundant,
and dixChangeWindowProperty() has been around since 1.5 so we can
safely use that.

The protocol still only supports 8859-1 though, so we need to
convert things to and from UTF-8.

Makes it easier to do requests from different parts of the code.

Also handle clipboard transactions from the server to the client
directly in the server without the help of vncconfig.

Handle the clipboard directly in the server, avoiding the
dependency on vncconfig. This commit adds support for clipboard
from the client to the server. Handling of the other direction
will follow.