Keep the X clipboard and the cutbuffer in sync
This tracks changes in the server's cutbuffer and clipboard
selection. when the clipboard is changed, it updates the
cutbuffer. When the cutbuffer is changed, it owns the clipboard
selection. The cutbuffer and clipboard selection are always
synchronized. In the case of a VNC client since it synchronizes the
Windows' clipboard and the server's cutbuffer, all three "clipboards"
are always kept synchronized. When you copy some text in Windows, the
cutbuffer and the clipboard selection are updated. When you copy text
on the server using either the cutbuffer or the clipboard selection,
the Windows's clipboard is always updated.
