All shebangs follow pep-394

Specifically they're pointed at `python2`, rather than simply `python`.

References to /usr/bin/python(2) have been changed to /usr/bin/env python2.

For reference:
http://python.org/dev/peps/pep-0394/
Non-scripts don't get shebangs
Merge pull request #745 from seandst/pep-394

pep-394 and shebang cleanup