Slow tests in LastModifiedFileComparatorTest

The setUp method uses a fairly inefficient method of using Thread.sleep() to produce the different file timestamps. As this method is run for every test, the tests in this class can take quite a while to run. On my system they were taking 13 seconds to run in total.

A faster way would be to just specify timestamps in the past and the future, so I changed them to select a time 1 hour in the past and 1 hour in the future. The new tests now pass and run in less than a second.