correct db_ prefix and remove use of None as default parameters
fix exercise url to handle different ports
change test_change_password_on_existing_user to try new password on
login
refactor ChangeLocalUserPassword.setUp to use create_student function
change test_change_password_on_nonexistent_user to try logging in with
old password
change browser_insert_answer to return accumulated points
Merge pull request #18 from aronasorman/KA_test

Accomodate suggestions from last pull request
So great to have your help on this!