[Bro] HTTP encoding

[Vern Paxson]

> I was testing some evasion techniques using HTTP unicode encoding, and I was
> surprised to see that Bro seems to completely miss the attacks in that case.

Indeed, it lacks a Unicode decoder :-(.  Morley Mao wrote one a while ago,
which unfortunately never got integrated.  I'd be happy to send it along
to someone who wants to bring it up to date (and I promise to integrate
the result!).

		Vern