best way of testing a program exists before using it?

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    Tim> All that said, I think the only thing would be to add a line to the
    Tim> docs saying sthg like: This will always return False for X_OK under
    Tim> Win32. I'm happy to submit the patch, but is it worth it?

Yes, please do.  If people think it works the same on Unix and Windows,
they'll get burned and just have to reproduce your investigative work to
figure out what happened.

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