check cheksum docopts in path can be python version and not golang compiled

[Sylvain303]

If you relay on $PATH to execute docopts and docopts is the python version, you get misbehavior.

Especially using bash wrapper doctops.sh which doesn't stop on -h.

So some checks should be added inside docopts.sh wrapper to detect wrong executable to avoid caller script to continue its execution. Which may be quite wrong if the scripts rely on docopts to naturally stops it execution on -h