Comment 22 for bug 230973

here is a patch that adds an UPnPManager, which creates a thread to do UPnP mappings. it silently fallbacks to other implementations if it has multiple impls.
i have kept UPnP_MiniUPnPc in win32/ for now - LinuxDC++ people can then adjust it to their needs and move it to dcpp/.

by default, windows builds will now be able to use both UPnP_MiniUPnPc and UPnP_COM, with a preference over UPnP_MiniUPnPc (so if it works, UPnP_COM will never be called).

regarding switching to passive for the very few seconds during which UPnP initialization lasts, i feel this would introduce more problems and i'd prefer to keep it the way it is: consider that the user is in active mode if she has selected UPnP in settings.
besides, when UPnP fails, there's an error message inviting the user to rectify her settings; this is better than silently selecting passive mode on her behalf.