[links] Drag 'n drop support!

[Edward Rosten]

> I haven't integrated it with the paste system yet. The mechanism for X11 
> copy/paste and DnD are almost identical, so links could get advanced pasting 
> quite easily as well.

The reason I have used a different method is because DnD support in other 
applications is somewhat unreliable compared to pasting (eg Konqueror 
keeps segfaulting). If DnD is implemented synchronusly (like the paste in 
links), then links will hang if the program on the other end crashes.

-Ed