Fix the primary issue with web sockets on Windows

@michaelbjames and @deadfoxygrandpa, turns out it was the deceptive
kind of bug :P The -threaded flag appears to be off by default on
Windows!
Try to be really careful and clear about cleaning up threads

@michaelbjames, I think this will stop the Notify manager more
reliably, but the way that library works is pretty mysterious to me. It
may not have even been a problem in the first place.
Get slider working in IE

IE does not register an ‘input’ event until the user lets go of the
slider, whereas it does trigger a ‘change’ event on every change. If I
remember correctly, this is actually the spec, and no one else follows
it. In any case, you gotta do it both ways for now.

cc’ing @michaelbjames, the kind of fact you’d rather not know!
Merge branch 'master' of https://github.com/elm-lang/elm-reactor

Conflicts:
	server/Socket.hs