[PATCH 2 of 2] revset: make optimizer use the new minusset

[Martin von Zweigbergk]

I'm new to the revset code, so please forgive me if the below makes no sense.

On Wed, Feb 10, 2016 at 4:23 PM, Durham Goode <durham at fb.com> wrote:
> # HG changeset patch
> # User Durham Goode <durham at fb.com>
> # Date 1455146394 28800
> #      Wed Feb 10 15:19:54 2016 -0800
> # Node ID ec633f772ea500d3db5e2fff3240099960f679b3
> # Parent  edfc4fda0c1ca78186d9a779f0d4d0cfc6e1c03f
> revset: make optimizer use the new minusset
>
> Now that we have a minusset class, we need to change the optimizer to use it.

It seems to me that these two patches do two things:

1) Tell the optimizer to use use the revset's '-' operator (i.e.
abstractsmartset.__sub__()) when the user used '-' in the expression.
These are the changes to revset.py in this patch, except for the the
hunk starting on line 2846.

2) Return your new minusset class when using revset's '-' operator.

>From what I can tell, step 1) makes a big difference on its own. On
the set of tests I ran, I did not see any benefit from step 2), but it
might be that I didn't run the relevant tests. Would it make sense to
restructure these patches into those two steps instead? It would be
nice to see timings showing improvements from both steps.

Also, please rename either the class or the function, so they're not
both called "minusset". I don't even know which one Python will pick
when they share a name.