Brought back the SPIActivator that I removed in r765974. Found out that it was needed after all, although its hard to test automatically since the system tests don't need it (probably because the Spring-DM system test framework does some of this already).
cxf/dosgi/trunk/distribution/single-bundle/src/main/java/org/apache/cxf/dosgi/singlebundle/AggregatedActivator.java