bugfix: python.el: completion in inferior python

[Martin Svenson]

Hello,

I've fixed a small "bug" that affects, among others, 
python-complete-symbol in the inferior python buffer.

Problem (and solution):
When doing python-complete-symbol in the inferior python buffer, emacs 
freezes. This is due to a while-loop in python-symbol-completions that 
never gets any input, because the python process signals an error that 
python-imports is nil (because we're not in an python-edit-buffer). The 
correct value of python-imports in an unknown context should not be nil 
(as in current version), but "None", which makes things work smoothly 
and as expected.

P.S. This is my first time sending a patch to an open-source project. I 
apolgize if my message does not conform with etiquette.

// Martin

*** python.el.old       Wed Jan 16 14:29:04 2008
--- python.el   Wed Jan 16 14:46:58 2008
***************
*** 1848,1854 ****
  
  ;;;; Completion.
  
! (defvar python-imports nil
    "String of top-level import statements updated by `python-find-imports'.")
  (make-variable-buffer-local 'python-imports)
  
--- 1848,1854 ----
  
  ;;;; Completion.
  
! (defvar python-imports "None"
    "String of top-level import statements updated by `python-find-imports'.")
  (make-variable-buffer-local 'python-imports)