This way the grabbing side can indicate when the clipboard owning app
can provide the clipboard contents in multiple formats, ie plain text
and html.
Also drop the VD_AGENT_CLIPBOARD_BITMAP type until we have a clear
cross platform definition of the contents to send for bitmap type
clipboard data.
-VD_AGENT_CLIPBOARD_GRAB(type) - tell the other side that an application in our side ("we") got ownership of the clipboard.
-VD_AGENT_CLIPBOARD_REQUEST(type) - after we know the other side owns the clipboard (GRAB received), we notify the os we are the owner. when we are asked by the os/app for the clipboard data, we send this REQUEST msg to the other side.
-VD_AGENT_CLIPBOARD(type, data) - the existing message for sending the clipboard, is now sent only in response to REQUEST.
-VD_AGENT_CLIPBOARD_RELEASE - tell the other side that we are no longer the owner of the clipboard (e.g. the owner app was closed).
this patch will be followed by agent & client patches handling the above messages.
