[Python-Dev] marking os.system() as deprecated in the docs

[A.M. Kuchling]

The current text is:

    The subprocess module provides more powerful facilities for
    spawning new processes and retrieving their results; using that
    module is preferable to using this function. See the Replacing
    Older Functions with the subprocess Module section in the
    subprocess documentation for some helpful recipes.

We could soften "using that module is preferable" to say "may be", or
just delete that whole clause completely.

--amk