Better error message with very old python

[tkittel]

One user reports getting this confusing error message when trying to run the pymcpltool with a very old and unsupported version of python, 2.4.3:

> File "./pymcpltool", line 31
>
>     _str = lambda s : s.encode('ascii') if (hasattr(s,'encode') and 
> bytes==str) else s
>
> ^
>
> SyntaxError: invalid syntax s.encode('ascii') if (hasattr(s,'encode') 
> and bytes==str) else s

The ternary operator is likely to blame here. We should see if we can improve the message.

[tkittel]

I think python 2.4 is now completely gone, so simply closing here.