'quit' and 'q' debugger command fixes

This pull:
- Makes 'quit' command do underlying pdb 'do_quit', rather than 'do_continue'.
- Make s'q' command restore stdout and stdin
- Makes EOF do underlying EOF action, rather than just 'continue'.
- Removes Python 2.5.2 (and presumably, 2.5 and 2.6 in general) incompatibility.