Changes largely merged in from Dave Love's code. Doc fixes.

Changes largely merged in from Dave Love's code.  Doc fixes.
(python-mode-map): Add python-complete-symbol.
(python-comment-line-p, python-beginning-of-string): Use syntax-ppss.
(python-comment-indent, python-complete-symbol)
(python-symbol-completions, python-partial-symbol)
(python-try-complete): New.
(python-indent-line): Remove optional arg.  Use python-block-end-p.
(python-check): Bind compilation-error-regexp-alist.
(inferior-python-mode): Use rx.  Move keybindings to top level.
Set comint-input-filter.
(python-preoutput-filter): Use rx.
(python-input-filter): Re-introduce.
(python-proc): Start new process if necessary.
Check python-buffer non-nil.
(view-return-to-alist): Defvar.
(python-send-receive): New.
(python-eldoc-function): Use it.
(python-mode-running): Don't defvar.
(python-mode): Set comment-indent-function.
Maybe update hippie-expand-try-functions-list.
(python-indentation-levels): Initialize differently.
(python-block-end-p): New.
(python-indent-line): Use it.
(python-compilation-regexp-alist): Augment.
(run-python): Import `emacs' module to Python rather than loading
code directly.  Set python-buffer differently.
(python-send-region): Use emacs.eexecfile.  Fix orig-start calculation.
Use python-proc.
(python-send-command): Go to end of comint buffer.
(python-load-file): Use python-proc, emacs.eimport.
(python-describe-symbol): Simplify interactive form.
Use emacs.help.  Do use temp-buffer-show-hook.
Call print-help-return-message.
(hippie-exp): Require when compiling.
(python-preoutput-continuation): Use rx.