[boost] [1.39.0] getting started update

The attached patch updates getting started to the changes I've did to simplify build process, described in: http://permalink.gmane.org/gmane.comp.lib.boost.devel/188461 and some other existing reality. Specifically: 1. The bootstrap + bjam procedure is documented. 2. The Boost.System library is added to the list of libraries needing compilation. 3. Unix docs are adjusted to use stage/lib everywhere, as opposed to using 'lib' in some cases. Dave, can you review this? I have regenerated HTML and visually inspected them, but HTML diffs are not included for clarity. Thanks, Volodya