move runtime/build/test prereq sync to finalize

Instead of running in register_prereqs, we hook before finalize so that
we only sync after all PrereqSources have run.  This is both more
efficient and avoids errors if plugins directly manipulate the
requirements.
improve runtime/build/test prereq sync test
v5.001

        [THIS RELEASE MIGHT BREAK YOUR BUILD]
        - typo fixes (thanks, David Steinbrunner)