Tiny fixes for compatibility with python 3 and numpy

Hi, I hope I'm doing this right - I've never used github before.  I just tried memprof and had two little issues: setup.py is broken in py3 due to assuming the result of filter is a list, and using an equality rather than identity check in this line in memprof.py fails with certain objects with a custom `__ne__` (e.g., numpy arrays, for which != generally returns an object that can't be converted to a bool).  Otherwise it's an awesome tool, thanks!