The clean_history management command to remove excess courseware_studentmodulehistory records.
Quiet some debug output, get transactions right.
Add batch and sleep arguments so we can control the speed from the command line.
Records should be sorted by created,id so that timestamp ties will be broken by id.
Use TransactionTestCase, to keep other tests from failing, even though it slows them down.
Only quiet the particular logger we think is too noisy.
Merge pull request #411 from edx/ned/studentmodulehistory-cleaner-command

Ned/studentmodulehistory cleaner command