Spelling: internalization --> internationalization

Fixed displays of the interactive prompt in running text.
These close SourceForge bug #115658.

Also:

Updated discussion of tuple unpacking to reflect the general ability
to unpack any sequence type.  Explained that it is possible to create
tuples which contain mutable values, and noted in the dictionary
section that such tuples cannot be used as keys.

Noted that .pyc and .pyo files can be run directly when provided as
the script parameter to the interpreter, and slightly clarified
comments about using modules with only the byte compiled code.

Removed some XXX comments that are no longer relevant.
Removed commented-out paragraph about __private names being experimental.

Adjusted markup for consistency in some places.