Merge branch 'jt/fetch-pack-negotiator'

Code restructuring and a small fix to transport protocol v2 during
fetching.

* jt/fetch-pack-negotiator:
  fetch-pack: introduce negotiator API
  fetch-pack: move common check and marking together
  fetch-pack: make negotiation-related vars local
  fetch-pack: use ref adv. to prune "have" sent
  fetch-pack: directly end negotiation if ACK ready
  fetch-pack: clear marks before re-marking
  fetch-pack: split up everything_local()

object.h

@@ -54,7 +54,8 @@ struct object_array {
 /*
  * object flag allocation:
  * revision.h:               0---------10                              2526
- * fetch-pack.c:             0----5
+ * fetch-pack.c:             01
+ * negotiator/default.c:       2--5
  * walker.c:                 0-2
  * upload-pack.c:                4       11----------------19
  * builtin/blame.c:                        12-13