Merge changes from Dave Love's v2007-Sep-10.

Merge changes from Dave Love's v2007-Sep-10.
(python-font-lock-keywords): Update to the 2.5 version of the language.
(python-quote-syntax): Let-bind font-lock-syntactic-keywords to nil.
(python-backspace): Only behave funny in code.
(python-compilation-regexp-alist): Add PDB stack trace regexp.
(inferior-python-mode): Add PDB prompt regexp.
(python-fill-paragraph): Refine the fenced-string regexp.
(python-find-imports): Handle imports spanning several lines.
(python-mode): Add `class' to hideshow support.