title: Reading a Multigraph in NetworkX from gml file
body: <p>I am attempting to read a gml file into a multigraph object; however, I am receiving the following error:</p>
  
  <pre><code>NetworkXError: edge #1 (0--3) is duplicated
  </code></pre>
  
  <p>In the gml file the the edge is duplicated:</p>
  
  <pre><code>  edge [
      source 0
      target 3
      LinkLabel "Green"
    ]
    edge [
      source 0
      target 3
      LinkLabel "Brown"
    ]
  </code></pre>
  
  <p>As I understand it, the read_gml function should return a multigraph when the input is a multigraph.  What am I missing?</p>