Bug 162655 [Undo] [IDE] - Undoing a delete should check for existence of resources to be restored
N20061027. - I deleted two projects (along with their content). I read the warning that undo delete cannot restore the content and said "OK." - Then I checked out those same projects from HEAD. - Then I selected "Undo Delete Resources." This overwrote my code with empty projects. I think that "Undo Delete Resources" should become invalid if the resources exist again, because you'll end up replacing content without keeping a backup.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/ide/undo/AbstractResourcesOperation.java
* Compute the status for deleting resources. A status severity of
	 * <code>OK</code> indicates that the delete is likely to be successful. A
	 * status severity of <code>ERROR</code> indicates that the operation is
	 * no longer valid. Other status severities are open to interpretation by
	 * the caller.
	 * 
	 * Note this method may be called on initial deletion of a resource, or when
	 * a create or delete operation is being undone or redone. Therefore, this
	 * method should check conditions that can change over the life of the
	 * operation, such as the existence of the resources to be deleted. One-time
	 * static checks should typically be done by the caller (such as the action
	 * that creates the operation) so that the user is not continually prompted
	 * or warned about conditions that were acceptable at the time of original
	 * execution.
	 */
	protected IStatus computeDeleteStatus() {
		if (resources == null || resources.length == 0) {
			markInvalid();
			return getErrorStatus(UndoMessages.AbstractResourcesOperation_NotEnoughInfo);
		}
		if (!resourcesExist()) {
			markInvalid();
			return getErrorStatus(UndoMessages.AbstractResourcesOperation_ResourcesDoNotExist);
		}
		return Status.OK_STATUS;
	}
	/**
	 * Set the array of resource descriptions describing resources to be
	 * restored when undoing or redoing this operation.
	 *