Bug 293787 Markers view not filtering by workingsets
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/MarkerContentGenerator.java
Collection enabled = getEnabledFilters();
		if (enabled.remove(group)) 
			group.setEnabled(false);
		else {
			group.setEnabled(true);
			enabled.add(group);
		}
		writeFiltersPreference();
		requestMarkerUpdate();
	}
	/**
	 * Update the filters.
	 * 
	 * @param filters
	 * @param
	 */
	void updateFilters(Collection filters, boolean andFilters) {
		setAndFilters(andFilters);
		this.filters = filters;
		enabledFilters = null;
		writeFiltersPreference();
		requestMarkerUpdate();
	}
	/**
	 * Set whether the filters are being ANDed or ORed.
	 * 
	 * @param and
	 */
	void setAndFilters(boolean and) {
		andFilters = and;