Fix issue #428

Added new performance.txt files for each test. Added delta operation count to performance logs. Fixed possible negative values on processing GetOperationCountCommand.

This should fix issue #428.
One of the principles we follow is the 'fail fast' principle. As soon as you start to learn about the name of a test case (so when it is loaded) you tell the user that it isn't valid. So I would also add a check to the loading of the test property file.