title: error when trying to import ps file by grImport in R
body: <p>I need to create a <em>pdf</em> file with several chart created by <code>ggplot2</code> arranged in a A4 paper, and repeat it 20-30 times. </p>
  
  <p>I export the <code>ggplot2</code> chart into <em>ps</em> file, and try to <code>PostScriptTrace</code> it as instructed in <code>grImport</code>, but it just keep giving me error of <code>Unrecoverable error, exit code 1</code>.</p>
  
  <p>I ignore the error and try to import and <em>xml</em> file generated into R object, give me another error:</p>
  
  <blockquote>
    <p>attributes construct error<br>
    Couldn't find end of Start Tag text line 21<br>
    Premature end of data in tag picture line 3<br>
    Error: 1: attributes construct error<br>
           2: Couldn't find end of Start Tag text line 21<br>
           3: Premature end of data in tag picture line 3</p>
  </blockquote>
  
  <p>What's wrong here?</p>
  
  <p>Thanks!</p>