Original Commit Messages:
use edx's own get_parent method, rather than our own.
add field to unique constraint to avoid MultipleObjectsReturned in case of multiple browser clicks on submit
fix 0011 migration, inherit from TimeStampedField and add composite index (migration only)
fix bug where adding an already registered user to a ccx would cause a crash due to an undefined variable
add assertNumQueries tests to test modules where override field providers are used
remove unnecessary teardown
implement recommended style for checking empty list
import utility methods rather than use duplicate code
added comment explaining date conversion to string for json
add logging for invalid users or emails when enrolling students
add comment about xmodule user state
avoid using get_or_create, which seems to be causing a race condition on schedule change save
relocate badly placed edvent handlers to fix multiple submit problem
b3da2a54bb