We cannot integrate this into our event loop like we planned, because
Wine a) grabs the mouse pointer so we cannot do that, and b) blocks the
GUI thread. So instead we will spawn our own thread and do polling based
XDND. When Wine's tracker window gets destroyed, we know that the left
mouse button has been released.
Apparently X11 connections are a scarce resource, so it seems like a
good idea to not hang on to them for too long. Now this is sort of a
hybrid between COM-style memory management and a singleton.
This doesn't do anything useful yet, but it will print the names of
files that are being dragged and dropped on the Wine server (using the
OLE API) while the plugin is open.