Bug 214648 [Markers] AttributeMarkerGroupings and GroupingEntries not being cleaned up on removal
We are still leaving the references to AttributeMarkerGroupings and GroupingEntries when we unload
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/views/markers/internal/MarkerGroup.java
/**
	 * Find the group value. If it cannot be found in an attribute mapping then
	 * return null;
	 * 
	 * @param concreteMarker
	 * @return String or <code>null</code>
	 */
	private MarkerGroupingEntry findGroupValue(ConcreteMarker concreteMarker) {
		String type = concreteMarker.getType();
		IMarker marker = concreteMarker.getMarker();
		return findGroupValue(type, marker);
	}
	/**
	 * Find the group for the marker of the specified marker type.
	 * 
	 * @param type
	 * @param marker
	 * @return MarkerGroupingEntry
	 */
	public MarkerGroupingEntry findGroupValue(String type, IMarker marker) {
		if (typesToMappings.containsKey(type)) {
			EntryMapping defaultMapping = null;
			Iterator mappings = ((Collection) typesToMappings.get(type))
					.iterator();
			while (mappings.hasNext()) {
				EntryMapping mapping = (EntryMapping) mappings.next();
				if (mapping.hasAttributes()) {
					MarkerGroupingEntry entry = mapping.testAttribute(marker);
					if (entry != null) {
						return entry;