[boost] new library boost.fiber in vault

I've re factored boost.fiber (-> boost vault http://www.boostpro.com/vault/index.php?&direction=0&order=&directory=Concurrent%20Programming). The library provides a so called lightweight thread of execution (also known as user-space thread or fiber on WIN32). The API is modeled after boost.thread. Beside a scheduler (currently simple round-robin) for the fibers the library provides sync. primitives like mutex, condition- and event-variables (auto-reset, manual-reset, count-down). Message can be passed between fibers via bounded-/unbounded-fifo. Some feedback would be nice. regards, Oliver