Update loaddata.py

Changed check for path separator so that paths are normalized on Windows, Mac and Linux. This allows relative paths to fixtures to be specified as '[path]/fixtures/[name].json' which is not currently working in Windows 8.1.

After running the test suite, I am getting 7295 tests passed, 8 expected failures and 684 skipped. 
Hmm. Not sure what happened there. Cursor focus might have jumped and I didn't notice. I'll revert the change.