[Python-3000] Line continuation using ellipsis

[Andrew Koenig]

> I'm not proposing to remove the feature, however I'd like to see an
> alternative method for declaring statements that cross a line boundary.
> I seem to recall at one point someone suggesting the use of ellipsis,
> which makes a lot of sense to me:
> 
>     sorted_result = partition_lower( input_list, pivot ) ...
>        + pivot ...
>        + partition_upper( input_list, pivot )

I once used a programming language named EFL that had what I think is a nice
convention: If the last token on a line is an operator (i.e. something that
cannot syntactically be the last token of a statement), the next line is
deemed a continuation.  So your example would be able to be written this
way:

	sorted_result = partition_lower( input_list, pivot) +
	   pivot +
	   partition_upper( input_list, pivot )

Interestingly, if I remember correctly, EFL did *not* assume a continuation
for unmatched parentheses -- it looked only at the last token on the line.

For Python, I guess I'd like it if either unmatched parentheses or ending
with an operator were to signal continuation.