Update and make more consistent the specification of Python package
building. Since SCons can be run by Python 3 now, we cannot assume that
the Python running SCons is Python 2. This changes a bunch of
assumptions in SConstruct about where things should be built or
installed. This commit addresses those assumptions by making the options
for Python 2 and Python 3 symmetric.
Replace distutils with setuptools in the Cython and python_minimal
interfaces. Add console_scripts option to generate OS specific scripts to run
ck2cti, mixmaster, and ctml_writer
Remove script files that are obsoleted by console_scripts from
setuptools. Remove installation of the script modules from SConstruct.
Fix Python installers so that when a prefix directory is specified on the
command line, setuptools doesn't throw an error. The setuptools documentation at
[1] prefers setting PYTHONUSERBASE rather than PYTHONPATH. Use normpath to avoid
bugs in setuptools on Windows [2]. Specify an empty "--prefix" if the compiler
is clang to fix a bug with Homebrew Python on Mac OSX [3].
[1]: https://pythonhosted.org/setuptools/easy_install.html#custom-installation-locations
[2]: http://stackoverflow.com/q/31629398
[3]: https://github.com/Homebrew/homebrew-python/issues/187
