title: xlrd detects cells as empty but they are not empty
body: <p>I have some values in my *.xls file but when I try to import them with wb_sheet.col_values(...) I only get empty values. I tried wb_sheet.col(...) and it also claims that those cells are empty. However, they are not, I can see the values in Excel.</p>
  
  <p>My *.xls file was generated by a Labview script and I am pretty sure it contains some makros and stuff. However, xlrd does not return an error.</p>
  
  <p>I would upload a sample sheet but it contains confidential information.</p>
  
  <p>Versions:
  python 2.7.3, Windows 7, Excel 2010, xlrd 0.8.0.</p>
  
  <p>Small script:</p>
  
  <pre><code>wb = open_workbook('*.xls')
  wbs = wb.sheet_by_index(0)
  wbs.col(0)
  </code></pre>
  
  <p>The result I get is <em>empty:'',</em> for all of the cells, even though the first column contains values, when I open with excel.</p>