title: Crontab error : Windows can not find the specified file
body: <p>I am trying to use this example script to test crontab in python:  </p>
  
  <pre><code>from crontab import CronTab
  
  tab = CronTab(user='www',fake_tab='True')
  cmd = '/var/www/pjr-env/bin/python /var/www/PRJ/job.py'
  cron_job = tab.new(cmd)
  cron_job.minute().every(5)
  #writes content to crontab
  tab.write()
  print tab.render()
  </code></pre>
  
  <p>It returns with an error 'fake_tab' not defined. If i remove this parameter and call the function<br>
  like this:  CronTab(user='www'). I returns the following error :  </p>
  
  <pre><code>Traceback (most recent call last):
  File "&lt;pyshell#8&gt;", line 1, in &lt;module&gt;
  tab = CronTab(user='www')
  File "C:\Python27\lib\site-packages\crontab.py", line 160, in __init__
  self.read(tabfile)
  File "C:\Python27\lib\site-packages\crontab.py", line 183, in read
  p = sp.Popen(self._read_execute(), stdout=sp.PIPE)
  File "C:\Python27\lib\subprocess.py", line 711, in __init__
  errread, errwrite)
  File "C:\Python27\lib\subprocess.py", line 948, in _execute_child
  startupinfo)
  WindowsError: [Error 2] The system cannot find the file specified
  </code></pre>
  
  <p>Does any one know, what am I missing?  </p>