Broken python-model.el

[Skip Montanaro]

    Brian> Wrong type argument: sequencep, cpython

    Thomas> I also get the above error when the file begins with

    Thomas>   #!/usr/bin/env

    Thomas> on Windows.  XEmacs 21.4 (patch 13), python-mode 4.29.
    Thomas> Removing this line fixes it.

Yeah, I can see where that would cause problems.
(py-choose-shell-by-shebang) really needs to see a valid #! line.  I'll see
if I can figure out a way to worm around this sort of breakage.

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