Some tests failed because the bootstrap would continue to run even
detecting a problem. This puts in the missing early return statements
in the boost-build builtin rule to get the short circuit on error
like the original Jambase.
This ports the minimal Jambase to native C++. This removes the need for
mkjambase and the Jambase files. To accomplish that it adds C++
utility wrapers around Jam language primitives. Which makes future
similar work much easier.
