manage.py: Give a nice error message if run as root on posix systems.

If the os is posix, this will check to see if the user is root and
alert them to run as zulip user if so.

Fixes #114.

manage.py

@@ -5,6 +5,9 @@ import logging
 import subprocess
 
 if __name__ == "__main__":
+    if 'posix' in os.name and os.geteuid() == 0:
+        from django.core.management.base import CommandError
+        raise CommandError("manage.py should not be run as root.")
     os.environ.setdefault("DJANGO_SETTINGS_MODULE", "zproject.settings")
 
     from django.conf import settings