Merge branch 'jk/mailmap-cleanup'

Update various entries in our .mailmap file.

* jk/mailmap-cleanup:
  contrib: update stats/mailmap script
  .mailmap: normalize emails for Linus Torvalds
  .mailmap: normalize emails for Jeff King
  .mailmap: fix broken entry for Martin Langhoff
  .mailmap: match up some obvious names/emails