Bug 318713 Duplicate toolbar items (navigate group)
SDK 4.0 - I20100701-1105. 1. start fresh workspace ==> navigate group appears twice which is quite confusing and wastes space.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/ContributionsAnalyzer.java
for (MMenuElement child : menuModel.getChildren()) {
			String elementId = child.getElementId();
			if (child instanceof MMenu && elementId != null) {
				existingMenuIds.add(elementId);
			} else if (child instanceof MMenuSeparator && elementId != null) {
				existingSeparatorNames.add(elementId);
			}
		}
		boolean done = toContribute.size() == 0;
		while (!done) {
			ArrayList<MMenuContribution> curList = new ArrayList<MMenuContribution>(toContribute);
			int retryCount = toContribute.size();
			toContribute.clear();
			for (MMenuContribution menuContribution : curList) {
				if (!processAddition(menuModel, menuContributionsToRemove, menuContribution,
						existingMenuIds, existingSeparatorNames)) {
					toContribute.add(menuContribution);
				}
			}
			
			
			done = (toContribute.size() == 0) || (toContribute.size() == retryCount);
		}
	}
	public static boolean processAddition(final MMenu menuModel,
			final ArrayList<MMenuElement> menuContributionsToRemove,
			MMenuContribution menuContribution, final HashSet<String> existingMenuIds,
			HashSet<String> existingSeparatorNames) {
		int idx = getIndex(menuModel, menuContribution.getPositionInParent());
		if (idx == -1) {