Bug 205049 Other plug-ins should be able to define default content generator
Currently only the content generator can define which plug-ins it can be the default for - we need a way for plug-ins to refer back to the marker support for thier own generator.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/views/markers/internal/MarkerSupportRegistry.java
while (nextEntriesIterator.hasNext()) {
					MarkerGroupingEntry next = (MarkerGroupingEntry) nextEntriesIterator
							.next();
					IDEWorkbenchPlugin
							.log(NLS
									.bind(
											"markerGroupingEntry {0} defines invalid group {1}",
											new String[] { next.getId(),
													nextGroupId }));
				}
			}
		}
	}
	/**
	 * Process the attribute mappings into thier required grouping entries.
	 * 
	 * @param attributeMappings
	 */
	private void processAttributeMappings(Collection attributeMappings) {
		Iterator mappingsIterator = attributeMappings.iterator();
		while (mappingsIterator.hasNext()) {
			AttributeMarkerGrouping next = (AttributeMarkerGrouping) mappingsIterator
					.next();
			String defaultEntryId = next.getDefaultGroupingEntry();
			if (defaultEntryId != null) {
				if (markerGroupingEntries.containsKey(defaultEntryId)) {
					MarkerGroupingEntry entry = (MarkerGroupingEntry) markerGroupingEntries
							.get(defaultEntryId);
					entry.setAsDefault(next.getMarkerType());
				} else {