[RFC] tsort.MergeSorter uses __slots__

[John Arbash Meinel]

Martin Pool wrote:
> That doesn't look substantially less clear, so if it is faster I'm +1
> to bring it in.
> 
> Is it faster to pass the values to the inner functions as default
> parameters, rather than letting them find it in the enclosing scope?
> I can imagine that it would be.
> 

Everything is being passed in as parameters. I just copied the old
(separate function) code, and then updated things like
"self._foo.append" to pass in the "self._foo.append" function as a variable.

I'll clean it up with a NEWS entry and merge it.

John
=:->