Enhancements on forward-sexp movement.

Enhancements on forward-sexp movement.
* progmodes/python.el (python-nav-beginning-of-statement)
(python-nav-end-of-statement): Return point-marker.
(python-nav-forward-sexp): lisp-like forward-sexp behavior.
(python-info-current-symbol)
(python-info-statement-starts-block-p): Rename from
python-info-beginning-of-block-p.
(python-info-statement-ends-block-p): Rename from
python-info-end-of-block-p.
(python-info-beginning-of-statement-p)
(python-info-end-of-statement-p)
(python-info-beginning-of-block-p, python-info-end-of-block-p):
New functions.