code: public int setValue(String xmlFilename, String xPath, String value) throws CmsXmlException {
  
          return setValue(getDocument(xmlFilename), xPath, value, null);
      }
docs: Sets the given value in all nodes identified by the given xpath of the given xml file.<p>
  
  If value is <code>null</code>, all nodes identified by the given xpath will be deleted.<p>
  
  If the node identified by the given xpath does not exists, the missing nodes will be created
  (if <code>value</code> not <code>null</code>).<p>
  
  @param xmlFilename the xml config file (could be relative to the base path)
  @param xPath the xpath to set
  @param value the value to set (can be <code>null</code> for deletion)
  
  @return the number of successful changed or deleted nodes
  
  @throws CmsXmlException if something goes wrong