function is overridden by a python version which accepts
  *either* a string (old behaviour) or a locale tuple.

- renamed a few methods (for consistency):

        get_locale => getlocale
        get_default_locale => getdefaultlocale
        set_to_default => resetlocale (!)

- the _locale implementation module can now implement
  an optional _getdefaultlocale function.  if that function
  isn't available, a POSIX-based approach is used (checking
  LANG and other environment variables, as usual).

(patch #100765)