Migration to Bordeaux-Threads-2

[kilianmh]

I would like to try the Hunchentoot migration to Bordeaux-Threads-2.

Mostly it should be straightforward. One question: can/should the symbol-macro *supports-threads-p* be dropped, since only multi-threaded implementations can load bordeaux-threads? Or keep it and set it to t by default? See #231

Any other comments on what to look after in this change?

[stassats]

What does BT2 bring for hunchentoot?

[jackcarrozzo]

Just active development and test coverage- see the link @kilianmh posted. Some added support for atomics and stuff but sounds like the api allows for a nearly 1:1 “port”, according to that post. Prolly a good idea.