Update for 1.6, refactor convert view to behave more like auth login view, make post-conversion login optional

There are 3 changes in this PR:
1. Swapped manage.py for a django 1.6 version
2. Reconfigured the "redirect_to" logic in the convert view to be more like the auth login view.  (A few lines of code have been copy/pasted from auth login).  Also, most importantly, allow specifying a post-convert URL in the settings file, like settings.LOGIN_REDIRECT_URL.  Added tests for this logic.
3. Allow disabling of automatic login after lazy user conversion via settings.AUTO_LOGIN_ON_LAZY_CONVERSION (with default to True).  Not sure how to test this - suggestions welcome.  

Overall, I undertook this set of changes to allow me to use lazysignup with django-registration's 2-step registration process (with email verification).  I think this solves issue #4 in a very minimal way.  (I plan to redirect users to the "Registration complete; now go check your email" view, and use the "converted" signal to send the email and create the RegistrationProfile instance - the activation code - required by django-registration).  I think a similar approach can be used for other verification workflows.