title: phpexcel pdf rendering library has not been defined
body: <p>After trying and failing to generate PDFs with PHPExcel 1.7.6 (out of memory errors), I upgraded to 1.7.8.  I can't for the life of me figure out how to get it working. I've tried tcPDF and mPDF, and it's the same for both.</p>
  
  <p>Putting it back to Excel output, I can see I'm setting the path correctly.  All I can get is "PDF Rendering library has not been defined", and I can't figure out what it wants - I've tried 'mPDF5.4', 'MPDF54' (the actual name of the folder itself), 'mpdf', 'mpdf.php'...same each time.</p>
  
  <p>I've been using PHPExcel for over a year, so I'm not entirely new to it.  I've lost way more time than I care to admit on this problem, and I haven't found this problem described anywhere, so I'm feeling more than a little stupid that I appear to be the only one that can't figure this out.</p>
  
  <p>The actual code I'm using is the following:</p>
  
  <pre><code>ini_set('include_path', ini_get('include_path').'\\Classes\\');
  
  $rendererName = PHPExcel_Settings::PDF_RENDERER_MPDF;
  $rendererLibrary = 'mPDF5.4';
  $rendererLibraryPath = ini_get('include_path') . $rendererLibrary;
  </code></pre>
  
  <p>(That is, pretty well a copy of the example code.)</p>
  
  <p>In the interest of completeness, the headers I'm using are </p>
  
  <pre><code>echo header("Content-Type: application/pdf");
  echo header("Content-Disposition: attachment; filename=".$filename.".pdf" );
  echo header('Cache-Control: max-age=0');
  </code></pre>
  
  <p>These near the top of the file, naturally.</p>
  
  <p>Near the end of the file, the output code is</p>
  
  <pre><code>$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'PDF');
  $objWriter-&gt;save('php://output');
  </code></pre>