title: Formula error in PHPExcel
body: <p>i have a strange issue with phpexcel on a pair of formulas and can't figure the source of the problem. (Other simple math formulas work, only this fails).</p>
  
  <p>Since the php report is quite long i'll get straight to the point.</p>
  
  <p>Setting this formula like this</p>
  
  <pre><code>$objPHPExcel-&gt;getActiveSheet()-&gt;setCellValue("D$cuenta_empleados", "=$'asientos_title'.K$cuadro_row" );
  </code></pre>
  
  <p>Throws me this</p>
  
  <pre><code>Fatal error: Uncaught exception 'Exception' with message 'INPUT NOMINA Agosto!D8 -&gt; Formula Error: An unexpected error occured' in /Users/PolCPP/Documents/Proyectos/Activos/beneficiat/php/inc/PHPExcel/Cell.php:293 Stack trace:
   #0 /Users/PolCPP/Documents/Proyectos/Activos/beneficiat/php/inc/PHPExcel/Writer/Excel5/Worksheet.php(455): PHPExcel_Cell-&gt;getCalculatedValue() 
   #1 /Users/PolCPP/Documents/Proyectos/Activos/beneficiat/php/inc/PHPExcel/Writer/Excel5.php(194): PHPExcel_Writer_Excel5_Worksheet-&gt;close() 
   #2 /Users/PolCPP/Documents/Proyectos/Activos/beneficiat/php/classes/Everything.class.php(2361): PHPExcel_Writer_Excel5-&gt;save('../../reports/1...') 
   #3 /Users/PolCPP/Documents/Proyectos/Activos/beneficiat/php/classes/Everything.class.php(3813): Everything-&gt;create_act_entry(Array, Array, Array, Array, Array) 
   #4 /Users/PolCPP/Documents/Proyectos/Activos/beneficiat/controllers/common/generar.php(68): Everything-&gt;gen_docs(Array, Array, Array) 
   #5 {main} thrown in /Users/PolCPP/Documents/Proyectos/Activos/beneficiat/php/inc/PHPExcel/Cell.php on line 293
  </code></pre>
  
  <p>So to debug it i remove the = to avoid it's calculation. I check it on openoffice. And i see </p>
  
  <pre><code>'ASIENTOS Agosto'.K4
  </code></pre>
  
  <p>And adding the = in front of it works.</p>
  
  <p>The second formula i have issues it's a condition one (same issue, it can generate it but it works on php)</p>
  
  <pre><code>=IF(D22&gt;O22;D22-O22;0)
  </code></pre>