[arch-general] simple trick to make dealing with python 2/3 scripts easier

[Ben Booth]

Lots of python scripts still use #!/usr/bin/python instead of explicitly 
stating which version of python to use. Here's quick trick to make running 
various python version 2 or 3 scripts easier:

remove the /usr/bin/python symlink and replace with this shell script:

#!/usr/bin/env bash
exec /usr/bin/"${PYTHON:-python3}" "$@"

Now you can set the PYTHON environment variable to be either python2 or 
python3, depending on which version of python the script expects. Just don't 
set PYTHON=python, or you'll get a recursive loop! The only problem with 
this approach is that /usr/bin/python is owned by the python package, so if 
you upgrade the python package it might create problems. Any one know of 
some way to work around this problem?