* lisp/progmodes/python.el: Add Ipython support (Bug#5390).

* lisp/progmodes/python.el: Add Ipython support (Bug#5390).
Based on a patch by Fabian Ezequiel Gallina.

(python-shell-prompt-alist)
(python-shell-continuation-prompt-alist): New options.
(python--set-prompt-regexp): New function.
(inferior-python-mode, run-python, python-shell): Require
ansi-color.  Use python--set-prompt-regexp to set the comint
prompt based on the Python interpreter.
(python--prompt-regexp): New var.
(python-check-comint-prompt)
(python-comint-output-filter-function): Use it.
(run-python): Use a pipe (Bug#5694).
(python-send-region): Send a different Python command if Ipython is in use.
(python-check-version): Use a Python command to find the version.