Quick and extremely dirty hacks to toggle between using CPython and

Quick and extremely dirty hacks to toggle between using CPython and
JPython interpreters.  This implementation may suck.

(py-jpython-command, py-jpython-command-args): New variables.

(py-mode-map): py-toggle-shells bound to C-c C-t

(py-toggle-shells): Command to toggle between using CPython (the
default) and JPython.  This is buffer local, and notice the mode-name
change.

(py-shell): Use either CPython or JPython.  Note that py-execute-*
still needs to be modified.