Make SelectorTransport.max_size _protected or move to constants.py

[GoogleCodeExporter]

In selector_events::SelectorTransport there's an undocumented but public class 
variable max_size that determines how large a buffer to pass to recv().  This 
shouldn't be public.

Original issue reported on code.google.com by [email protected] on 26 Nov 2013 at 8:55