On Unix-based systems, you can directly execute a script and the system
will automatically run it through its associated interpreter. However,
on Windows this does not work. You just get an error about the script,
which is just a text file, being an invalid executable.
This was an issue when running pyexpander. Now, Python is called
directly for pyexpander.
Although we cannot expect every developer to have pyexpander, for those
that do the build will automatically run it and check the expanded file
in the source code. If they match, a descriptive error is given.
We don't automatically update the file because subtle problems might
occur. It is better to alert a developer to fix the problem properly.
