Get the path to the playitagainsam command-line script.

def get_pias_script(environ=None):
    """Get the path to the playitagainsam command-line script."""
    if os.path.basename(sys.argv[0]) == "pias":
        return sys.argv[0]
    filepath = find_executable("pias", environ)
    if filepath is not None:
        return filepath
    filepath = os.path.join(os.path.dirname(__file__), "__main__.py")
    # XXX TODO: check if executable
    if os.path.exists(filepath):
        return filepath
    raise RuntimeError("Could not locate the pias script.")