While Wikipedia would lead you to be believe one thing...
... specifically that the vnd.microsoft.icon mime type is correct..
Well that's wrong.
It does work in the address bar, IE can also use an .ico file as an
<img src> in some cases. But it has to be served as image/x-icon
So thanks a lot wikipedia & jimmy wales' face. Psh.
Thanks a bunch Jonathan Neal. Fixes #219