When choosing Jinja2 as the template and sqlite as the database 
during the tracker creation (roundup-admin install), the resulting 
config.ini file does not include the database backend declaration.  
As the user tries to initialize the tracker (roundup-admin 
initialize), they get an error:  

  File "/usr/bin/roundup-admin", line 3, in <module>
    run()
  File "/usr/lib/python2.7/site-
packages/roundup/scripts/roundup_admin.py", line 49, in run
    sys.exit(tool.main())
  File "/usr/lib/python2.7/site-packages/roundup/admin.py", line 
1635, in main
    ret = self.run_command(args)
  File "/usr/lib/python2.7/site-packages/roundup/admin.py", line 
1504, in run_command
    return self.do_initialise(self.tracker_home, args)
  File "/usr/lib/python2.7/site-packages/roundup/admin.py", line 
526, in do_initialise
    tracker = roundup.instance.open(tracker_home)
  File "/usr/lib/python2.7/site-packages/roundup/instance.py", line 
327, in open
    return Tracker(tracker_home, optimize=optimize)
  File "/usr/lib/python2.7/site-packages/roundup/instance.py", line 
92, in __init__
    self.backend = backends.get_backend(rdbms_backend)
  File "/usr/lib/python2.7/site-
packages/roundup/backends/__init__.py", line 42, in get_backend
    module = __import__(module_name, vars)
ImportError: No module named back_

The error goes away after adding the line to the tracker's 
config.ini:
# Database backend.
# Default:
backend = sqlite