title: batik - id-attribute occurs twice in saved document
body: <p>I use Batik two load one svg-document and add an element form another
  document to it, but the id-attribute occurs in the saved document in some attributes now 
  twice. So when I'am trying to open the saved document with Inkscape, it just shows an error,
  that it couldn't open the file. By deleting some of the ids manually, the file now can be open with Inkscape.</p>
  
  <p>Thank you very much for your help.</p>
  
  <p>...  </p>
  
  <pre><code>try {
   // Load the basic symbol
   String parser = XMLResourceDescriptor.getXMLParserClassName();
   SAXSVGDocumentFactory f = new SAXSVGDocumentFactory(parser);
   Document documentBasicSymbol = f.createSVGDocument(imgFileBasicSymbol.toURI().toString());
  
  
   // Set the fill color of the basic symbol to symbolColor
   Element element = documentBasicSymbol.getElementById("basic_symbol");
   setSymbolFillColor(element, symbolColor);
  
  
   // Load the supplementary symbol
   Document documentSupplemtarySymbol =    
  f.createDocument(imgFileSupplementarySymbol.toURI().toString());
  
  // Add it to the basic symbol:
  Node nodeSupplementarySymbol = documentBasicSymbol.importNode(documentSupplemtarySymbol.getElementById("supplementary_symbol"), true);
         documentBasicSymbol.getDocumentElement().appendChild(nodeSupplementarySymbol);
  
  storeDocument(documentBasicSymbol, "SuppElementZuBasic.svg");
  </code></pre>
  
  <p>...</p>
  
  <p>part of the document:</p>
  
  <pre><code>xmlns:xlink="http://www.w3.org/1999/xlink"
  xmlns:svg="http://www.w3.org/2000/svg" zoomAndPan="magnify"
  contentStyleType="text/css" id="svg2" height="100"
  preserveAspectRatio="xMidYMid meet"
  xmlns="http://www.w3.org/2000/svg" id="svg2" version="1.2"&gt;
    &lt;g id="layer1" id="layer1"
    transform="translate(1.4982643,1.4982643)"&gt;
      &lt;rect x="64.599998" y="29.674999" width="67.803474"
      style="fill:blue;stroke:#000000;stroke-width:2.0965271;stroke-miterlimit:4;stroke-opacity:1;stroke-dasharray:none"
      height="37.653473" id="basic_symbol" id="basic_symbol" /&gt;
    &lt;/g&gt;
    &lt;path d="m 116.10938,37.703125 0,10.8125 -47.531255,0 0,2.40625 47.531255,0 0,4.5 0,0.59375 0.90625,0.28125 13.49999,6 0.3125,-0.875 0.59375,-0.90625 -13.21874,-5.75 0,-17.0625 -2.09375,0 z"
    id="supplementary_symbol"
    style="fill:#000000;fill-opacity:1;fill-rule:nonzero;stroke:none"
    id="supplementary_symbol" /&gt;
  </code></pre>