title: Django with lettuce and splinter, opens the browser but doesn't show anything
body: <p>I am trying my hands on lettuce with splinter. I have a django app which is well configured, no issues with that. When i try running lettuce, with the step which "should" visit a url in the browser, it doesn't returns any error but it doesn't shows up the page. </p>
  
  <p>Here is my .feature file :</p>
  
  <pre><code>Feature: A test 
  Scenario: User enters email, ajax will check if it exists
      When I go to the "/home/login/" URL 
      Then I fill in "#id_email" with "abc@def.gih"
  </code></pre>
  
  <p>here is my steps.py</p>
  
  <pre><code>from lettuce import *
  from lettuce.django import django_url
  from lxml import html
  from django.test.client import Client
  from nose.tools import assert_equals
  from splinter.browser import Browser
  from django.test.utils import setup_test_environment, teardown_test_environment
  from django.core.management import call_command
  from django.db import connection
  from django.conf import settings
  
  @before.all
  def set_browser():
      setup_test_environment()
      world.browser = Browser('firefox')
  
  @step(u'I go to the "(.*)" URL')
  def i_go_to_the_url(step, url):
      world.response = world.browser.visit(django_url(url))
  
  @step(u'I fill in "(.*)" with "(.*)"')
  def i_fill_in(step, field, value):
      world.browser.fill(field, value)
  </code></pre>
  
  <p>It opens the browser, the browser doesn't shows up anything but the test succeeds, and the second case fails with the following error : </p>
  
  <pre><code>Feature: A test        # candidate/feature/index.feature:1
  
    Scenario: User enters email, ajax will check if it exists # candidate/feature/index.feature:3
      When I go to the "/home/login/" URL             # home/feature/index-steps.py:29
      Then I fill in "email" with "dsfdf@safsdfsd"       # home/feature/index-steps.py:39
      Traceback (most recent call last):
        File "/usr/local/lib/python2.6/dist-packages/lettuce/core.py", line 117, in __call__
          ret = self.function(self.step, *args, **kw)
        File "********/candidate/feature/index-steps.py", line 40, in i_fill_in
          world.browser.fill(field, value)
        File "/usr/local/lib/python2.6/dist-packages/splinter/driver/webdriver/__init__.py", line 240, in fill
          field.value = value
        File "/usr/local/lib/python2.6/dist-packages/splinter/driver/webdriver/__init__.py", line 306, in _set_value
          self._element.clear()
      AttributeError: 'NoneType' object has no attribute 'clear'
  
  1 feature (0 passed)
  1 scenario (0 passed)
  2 steps (1 failed, 1 passed)
  (finished within 15 seconds)
  </code></pre>
  
  <p>Please can anyone help me on this ? </p>