[PATCH 4 of 4] revset: factor out public optimize() function from recursion

[Sean Farley]

Yuya Nishihara <yuya at tcha.org> writes:

> # HG changeset patch
> # User Yuya Nishihara <yuya at tcha.org>
> # Date 1462158540 -32400
> #      Mon May 02 12:09:00 2016 +0900
> # Node ID ab27ea196841de780186db4d25ed7b7e1b42625e
> # Parent  623d1c438bfe30c0937cb16f7a1873f22e6ae4a0
> revset: factor out public optimize() function from recursion
>
> New optimize() hides internal arguments and return values. This makes it easy
> to add more parameters and return values to _optimize().

Sure, looks good to me.