Merge branch 'lt/rev-list' into next

Merge branch 'lt/rev-list' into next

* lt/rev-list:
  setup_revisions(): handle -n<n> and -<n> internally.
  git-log (internal): more options.
  git-log (internal): add approxidate.
  Rip out merge-order and make "git log <paths>..." work again.
  Tie it all together: "git log"
  Introduce trivial new pager.c helper infrastructure
  git-rev-list libification: rev-list walking
  Splitting rev-list into revisions lib, end of beginning.
  rev-list split: minimum fixup.
  First cut at libifying revlist generation