Include required antl3 library and check if datastore is available
The datastore is checked for availability before requesting it to
be cleared. This is because gaeftest uses its own method for ensuring
no leakage of data by providing a temporary file as the backend.
Reviewed by: Sverre Rabbelier
Coverage: code coverage testing for Python
Coverage.py is a Python module that measures code coverage during test execution.
It uses the code analysis tools and tracing hooks provided in the Python standard
library to determine which lines are executable, and which have been executed.
For more information, see http://nedbatchelder.com/code/modules/coverage.html