Bug 203838 [Markers] [Markers] clicking on column headers does not sort table
I20070918 Clicking on any of the column headers does not sort based on the relevant column.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/provisional/views/markers/CachedMarkerBuilder.java
* 
	 * @return boolean <code>true</code> if the markers have not been
	 *         calculated.
	 */
	public boolean hasNoMarkers() {
		return currentMap == null;
	}
	/**
	 * Return whether or not the receiver is building.
	 * 
	 * @return boolean
	 */
	boolean isBuilding() {
		return building;
	}
	/**
	 * Schedule an update of the markers with a delay.
	 * 
	 */
	void scheduleMarkerUpdate() {
		cancelJobs();
		progressService.schedule(markerProcessJob, SHORT_DELAY);
	}
	
	/**
	 * Set the category group.
	 * @param group {@link MarkerGroup} or <code>null</code>.
	 */
	void setCategoryGroup(MarkerGroup group) {
		generator.setCategoryGroup(group);