--help changes

Hi,
some time ago, in

	http://thread.gmane.org/gmane.comp.lib.boost.build/9365/

we've discussed how to improve the --help output. I think
we've reached
an agreement, but nothing was implemented.

I've just committed the attached, that moves us close to the
ideal.
I also attach two example output -- for boost and for
example/hello.
In the latter case, there's some bogus project help printed,
but otherwise
everything seems good to me.

I've renamed --help-all to --help-internal per the above
discussion.

- Volodya

Boost.Build V2 (Milestone 11)
Boost.Jam 03.1.14

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