OSMF SVN

- Bubble metadata events up through CompositeElements.
- Change default synthesizer's behavior in parallel to return the first child metadata (regardless of whether multiple children have metadata in that namespace). Although a proper synthesizer is needed in this case, if none is provided it's better to return something than nothing.
- Add some guards around the parallel MBR trait, so that it doesn't RTE when it's the last one removed.
- Reenable some parallel unit tests that had been commented out.