Added tearDown() function to ensure that crawler is shut down after
each test.
Subclassed unittest.TestCase to add expected() method, which shows the
difference between the expected and actual value.
Lots of tweaks and additions to test cases.
Delete and re-import plugin if plugin dir changes.
Tests for time_to_fire().
Organize the tests a little better, so they call all be run with one
command ("all_tests"). Added tests for util.py. Make sure everyone
uses the same python.