Log Message:
Fix build of boost on DragonFly.
(a) bjam should be consistent with the rest of the world, the OS is
called DragonFly, not DragonFlyBSD. It might be _annoying_, but it is
a fact of live and no spelling fault can avoid it.
(b) disable the compiler thread support checks, they don't really work
and are not needed anyway.
(c) DragonFly has wchar and ctype functions, so use them.

Bump revisions of boost-build (bjam), boost-headers (well, they changed)
and boost-libs.