Add coveralls.io support.
Merge pull request #78 from pmclanahan/add-coveralls

Add coveralls.io support.
Omit test files from coverage report.
Update vendor to upgrade to Django 1.5.2.
Bug 875369 - Log failed Basket tasks

When a basket task is unable to complete (after exhausting its allowed
retries), log the task name, parameters, and whatever exception made
it fail into a database table where we can look at it later.