Python 3 compatibility

[petebachant]

This is probably not possible at the moment, since SCons does not yet support Python 3, though some progress can be made towards compatibility with both 2.7 and 3+. The first would be to add to the top of each Python file

from __future__ import division, print_function

Then put args for calls to print in parentheses.

More information: http://python-future.org/compatible_idioms.html

It would be helpful if there were tests in the Python package, or maybe just a script that imports all modules and scripts to check for syntax/import errors.

[Chris Sideroff]

CPL provides compatibility with Python 3 (http://caelus.readthedocs.io) and we will test/support SCons 3 for the 9.04 release of Caelus.