Add python version check

[sbp]

@dpk was getting an os.fsencode error.

[sbp]

Note that this needs to be done for scripts too. For example, if you use a local python to start saxo:

~/Python-3.3.2/python ./saxo -f start

But your /usr/bin/env python3 is less than 3.3, then you'll get command errors for those that use #!/usr/bin/env python3 as a shebang.

[sbp]

We could sniff to see what python executable is being used, then add that to $PATH.

[sbp]

The version check could also be made in @saxo.pipe.

[sbp]

A related fix is making sure that saxo versions match too. I've added a check for that in 4eb0ca843.