Moved pandas version dependency up to 0.14.1 because at some 
point read_csv stopped automatically parsing strings such as "yes" and
"no" as True and False.  Fixed tests for new behaviour.
Improved tree matcher error message.
Renamed integration_tests.py to test_integration.py so that test 
runners can find it (it was already found by nose, but not by the default
test runner in PyCharm).