Thread: continue the future.hpp renaming using shared_state.

svn path=/trunk/boost/thread/; revision=84590
Thread: fix packaged_task<void()> issue and add tests.

svn path=/trunk/boost/thread/; revision=84597
Thread: fix shared_future::get when the shared state is async; refactor the shared_state classes.

svn path=/trunk/boost/thread/; revision=84607
Thread: update history and fix typo on strict_lock.

svn path=/trunk/libs/thread/; revision=84628