Fixed #2073 -- Improved 'manage.py shell' not to pass argv to IPython if it's...

Fixed #2073 -- Improved 'manage.py shell' not to pass argv to IPython if it's installed. Thanks, jpellerin@gmail.com

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3069 bcc190cf-cafb-0310-a4f2-bffc1f526a37