test_since.py: support Python 3
test_since.py: support Python 3

- Use normWatchmanFileList everywhere.
- Use decodeBSERUTF8 to decode BSER-returned bytestrings where suitable.

dhruvsinghal/watchman,nodakai/watchman,dhruvsinghal/watchman,kwlzn/watchman,nodakai/watchman,dhruvsinghal/watchman,facebook/watchman,facebook/watchman,wez/watchman,wez/watchman,wez/watchman,wez/watchman,nodakai/watchman,dhruvsinghal/watchman,wez/watchman,kwlzn/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,kwlzn/watchman,nodakai/watchman,wez/watchman,facebook/watchman,wez/watchman,facebook/watchman,kwlzn/watchman,wez/watchman,facebook/watchman,kwlzn/watchman,dhruvsinghal/watchman,facebook/watchman,dhruvsinghal/watchman,kwlzn/watchman,kwlzn/watchman,nodakai/watchman,dhruvsinghal/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,dhruvsinghal/watchman,nodakai/watchman