Fix for Issue #73 + Tests

Same fix for Issue #73 to DateTimeValidationSpec.js as @swoodman already provided...

Also fixed copy/paste issues in DateTimeValidationFixtures.js, added some tests for valid 24 hour times with zero hours, shuffled some existing valid zero hour times from the InvalidTime to the ValidTime arrays. All the tests in DateTimeValidationFixtures.js should now run.

Apologies if I've made any rookie github faux pas - this is my first pull request!