title: Problem exporting an xls file for user download with django and HttpResponse
body: <p>I'm currently creating a spreadsheet using xlwt and trying to export it out as an HttpResponse in django for a user to download. My code looks like this:</p>
  
  <pre><code>response = HttpResponse(mimetype = "application/vnd.ms-excel")
  response['Content-Disposition'] = 'attachment; filename = %s +".xls"' % u'Zinnia_Entries'
  work_book.save(response)
  return response
  </code></pre>
  
  <p>Which seems to be the right way to do it, but I'm getting a:</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\dev\workspace-warranty\imcom\imcom\wsgiserver.py", line 1233, in communicate
      req.respond()
    File "C:\dev\workspace-warranty\imcom\imcom\wsgiserver.py", line 745, in respond
      self.server.gateway(self).respond()
    File "C:\dev\workspace-warranty\imcom\imcom\wsgiserver.py", line 1927, in respond
      response = self.req.server.wsgi_app(self.env, self.start_response)
    File "C:\dev\workspace-warranty\3rdparty\django\core\servers\basehttp.py", line 674, in __call__
      return self.application(environ, start_response)
    File "C:\dev\workspace-warranty\3rdparty\django\core\handlers\wsgi.py", line 252, in __call__
      response = middleware_method(request, response)
    File "C:\dev\workspace-warranty\imcom\imcom\seo_mod\middleware.py", line 33, in process_response
      response.content = strip_spaces_between_tags(response.content.strip())
    File "C:\dev\workspace-warranty\3rdparty\django\utils\functional.py", line 259, in wrapper
      return func(*args, **kwargs)
    File "C:\dev\workspace-warranty\3rdparty\django\utils\html.py", line 89, in strip_spaces_between_tags
      return re.sub(r'&gt;\s+&lt;', '&gt;&lt;', force_unicode(value))
    File "C:\dev\workspace-warranty\3rdparty\django\utils\encoding.py", line 88, in force_unicode
      raise DjangoUnicodeDecodeError(s, *e.args)
  DjangoUnicodeDecodeError: 'utf8' codec can't decode byte 0xd0 in position 0: invalid continuation byte. You passed in 
  </code></pre>
  
  <p>(I left off the rest because I get a really long line of this \xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1\x00 kind of stuff)</p>
  
  <p>Do you guys have any ideas on something that could be wrong with this? Is is it because some of my write values look like this:</p>
  
  <p>work_sheet.write(r,#,information) where information isn't cast to unicode?</p>