[todo.py] done.txt non existent

Hi Shane, Gina,

About
http://todotxt.com/library/todo.sh/todo.py


When the done.txt file is non existant because no tasks have been  
done yet, the report command  exit with an error.

% ls /Users/karl/todo
todo.txt

% python todo.py report
Traceback (most recent call last):
   File "todo.py", line 337, in <module>
     report()
   File "todo.py", line 263, in report
     archive()
   File "todo.py", line 161, in archive
     done = getDoneDict()
   File "todo.py", line 121, in getDoneDict
     for line in open(DONE_FILE).readlines():
IOError: [Errno 2] No such file or directory: '/Users/karl/todo/ 
done.txt'


You could refactor the program with
	try, except methods.

Here a diff for one rewritten function.

Best Regards.

-- 
Karl Dubost - http://www.w3.org/People/karl/
W3C Conformance Manager, QA Activity Lead
   QA Weblog - http://www.w3.org/QA/
      *** Be Strict To Be Cool ***