[boost] Stop on first error

Presently, when building Boost, the build process does not stop if an error has occurred. This is behaviour we inherited, and it differs from every other build system out there. We had quite a number of users confused where build ends with "failed N targets", with the original error scrolled away -- it is not apparent what has caused the error, and often, the error is not even available from console program history. While experienced users might prefer being able to kick a build, go to lunch, and then fix a couple of failures in the middle of the build, ordinary users don't like it so much. So, how about we do what the rest of the world does, and stop build of C++ Boost on the first error? Comments? - Volodya