genie_python: warn is unchanged script loaded again

Users sometimes forget to "save" before reloading a script, the work done in #2564 helps here but if a lot of editing is being done in a short time maybe the date mismatch will be missed. Could genie python load_script() keep a dictionary of { "lowercased absolute file path" : "last file modification" } so that is a file is loaded that is unchanged since the previous load a warning is printed.