Backport fixes for Bug#5390 and Bug#5694 from trunk.

Backport fixes for Bug#5390 and Bug#5694 from trunk.

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