Update Django dependency to 1.4.1+

setup.py

@@ -25,7 +25,7 @@ setup(name='django-oscar',
       packages=find_packages(exclude=["sandbox*", "tests*"]),
       include_package_data=True,
       install_requires=[
-          'django==1.4',
+          'django>=1.4',
           'PIL==1.1.7',
           'South==0.7.3',
           'django-extra-views==0.2.0',