Add a simple access check for a picker
The picker page should not be accessible if the required GET args are
not present.
Patch 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