[bind10-dev] require libboost_thread?

[Evan Hunt]

> But I think the fact that we once tried to require a compiled boost
> library warrants a discussion.  Are we planning to use the boost
> thread library eventually?

Note that the headers-only version of asio includes its own thread
implementation, asio::thread, which may be adequate for our future
thread API needs.

If we ever do decide it's worthwhile to use boost::thread, though,
then we should probably also make the switch to boost::asio, because
the primary reason for using the non-boost version is to avoid having
to link with an external boost library.

                                        eh