Database syncronization

[timothyhollabaugh]

The server creates a new thread for each request. Database access right now is not synchronized between requests. This can cause some funny business to happen, especially when the server is loaded and requests take a while. For example, if a test is submitted, but the registration is removed after the submit function checks for the registration but before it finishes grading the test. It would probably be best to use SQL row locks to ensure each item in the database is only touched by one request at a time.