Bug 299438 [CommonNavigator] CNF viewer state non properly reset when NCEs are activated or deactivated
The map of the objects to the NCEs should be reset whenever the NCEs associated with the viewer to change to avoid having stale label information. This has shown up when looking at the CNF tests that change the viewer.
tests/org.eclipse.ui.tests.navigator/src/org/eclipse/ui/tests/navigator/LabelProviderTest.java
public LabelProviderTest() {
		_navigatorInstanceId = "org.eclipse.ui.tests.navigator.OverrideTestView";
	}
	private static final int NONE = 0;
	private static final int OVERRIDDEN = 1;
	private static final int OVERRIDING = 2;
	private static final int BOTH = 3;
	private static final boolean BLANK = true;
	private static final boolean NULL = false;
	private static final String PLAIN = "Plain";
	private void setBlank(String cpToGet, boolean blank) {
		NavigatorContentExtension ext = (NavigatorContentExtension) _contentService
				.getContentExtensionById(cpToGet);
		TestLabelProvider tp = (TestLabelProvider) ext.getLabelProvider();
		if (blank)
			tp._blank = true;
		else
			tp._null = true;
	}
	
	
	
	public void blankLabelProviderOverride(int nce, boolean blank, String suffix) throws Exception {
		String overriddenCp = TEST_CONTENT_OVERRIDDEN1 + suffix; 
		String overrideCp = TEST_CONTENT_OVERRIDE1 + suffix; 
		String checkColor = "Green";
		switch (nce) {
		case NONE:
			break;