New faster Imenu implementation.

New faster Imenu implementation.

* lisp/progmodes/python.el:
(python-imenu-prev-index-position):
(python-imenu-format-item-label-function)
(python-imenu-format-parent-item-label-function)
(python-imenu-format-parent-item-jump-label-function):
New vars.
(python-imenu-format-item-label)
(python-imenu-format-parent-item-label)
(python-imenu-format-parent-item-jump-label)
(python-imenu--put-parent, python-imenu--build-tree)
(python-imenu-create-index, python-imenu-create-flat-index)
(python-util-popn): New functions.
(python-mode): Set imenu-create-index-function to
python-imenu-create-index.

* test/automated/python-tests.el (python-imenu-prev-index-position-1):
Removed test.
(python-imenu-create-index-1, python-imenu-create-flat-index-1):
New tests.

Fixes: debbugs:14058