Sunsetter improvements
Sunsetter improvements

Improve sunsetter output and behavior, especially in
positions close to mate.

- fix eval sign in "analyze" mode, which is
  used after sunsetter plays a forced move
- enter analyze mode if sunsetter quickly picks an obvious move
  without fully evaluating. For example, if alternatives allow
  mate in 1, sunsetter might move with only depth 1 evaluation,
  giving the best move but an incorrect eval score.
- approximate depth when sunsetter finds mate but doesn't give
  a depth.

Fixes #2198 and #2199.

clarkerubber/lila,clarkerubber/lila,luanlv/lila,arex1337/lila,arex1337/lila,clarkerubber/lila,clarkerubber/lila,luanlv/lila,arex1337/lila,arex1337/lila,clarkerubber/lila,clarkerubber/lila,luanlv/lila,clarkerubber/lila,arex1337/lila,luanlv/lila,luanlv/lila,arex1337/lila,luanlv/lila,luanlv/lila,arex1337/lila