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/MarkerSupportRegistry.java
* 
	 * @param marker
	 * @return String or <code>null</code>
	 */
	public String getCategory(IMarker marker) {
		try {
			return getCategory(marker.getType());
		} catch (CoreException e) {
			MarkerSupportInternalUtilities.handle(e);
		}
		return null;
	}
	/**
	 * Get the category associated with markerType. Return <code>null</code>
	 * if there are none.
	 * 
	 * @param markerType
	 * @return String or <code>null</code>
	 */
	public String getCategory(String markerType) {
		if (categories.containsKey(markerType)) {
			return (String) categories.get(markerType);
		}
		return null;
	}
	/**
	 * Return the TableSorter that corresponds to type.
	 * 
	 * @param type
	 * @return TableSorter