build files assume python is python2

On arch, python is python3.
I had to hack around my system to make it run with a dummy python script like this:

``` bash
/usr/local/bin/python
#!/bin/bash
script=$(readlink -f -- "$1")
case "$script" in (/path/to/project1/*|/path/to/project2/*|/path/to/project3*)
    exec python2 "$@"
    ;;
esac

exec python3 "$@"
```
