Khan/khan-exercises — pull request #7419 by divad12 (2011-12-01 02:56:04+00:00)
Title: Send attempt problem and hint requests in serial to avoid server-side race condition.

@kamens @kohlmeier Changes that we discussed which should fix the phantom-user multiple identities created issue for the full_solution hints A/B test alternative, as well as the race condition where multiple requests that write to the same UserExercise object are sent near-simultaneously.

Please review. Thanks!