Bug 25768 Package Explorer flashes too much on refresh and delete
build I20021105 - extracted a zip containing 22 non-Java files (.mxsd files from Dejan) into org.eclipse.ui - in Package Explorer, refreshed org.eclipse.ui - it flashed alot while refreshing - selected the 22 files and deleted them - it flashed even more
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerContentProvider.java
fViewer= (TreeViewer)viewer;
		if (oldInput == null && newInput != null) {
			JavaCore.addElementChangedListener(this); 
		} else if (oldInput != null && newInput == null) {
			JavaCore.removeElementChangedListener(this); 
		}
		fInput= newInput;
	}
	
	/**
	 * Processes a delta recursively. When more than two children are affected the
	 * tree is fully refreshed starting at this node. The delta is processed in the
	 * current thread but the viewer updates are posted to the UI thread.
	 */
	public void processDelta(IJavaElementDelta delta) throws JavaModelException {
		int kind= delta.getKind();
		int flags= delta.getFlags();
		IJavaElement element= delta.getElement();
		
		if (!fIsFlatLayout && element.getElementType() == IJavaElement.PACKAGE_FRAGMENT) {
			fPackageFragmentProvider.processDelta(delta);
			IJavaElementDelta[] affectedChildren= delta.getAffectedChildren();			
			processAffectedChildren(affectedChildren);
			return;
		}
			
		if (!getProvideWorkingCopy() && isWorkingCopy(element))
			return; 
		if (element != null && element.getElementType() == IJavaElement.COMPILATION_UNIT && !isOnClassPath((ICompilationUnit)element))
			return;