A random collection of style fixes and minor doc updates.

* fc/trivial:
  setup: trivial style fixes
  run-command: trivial style fixes
  diff: trivial style fix
  revision: trivial style fixes
  pretty: trivial style fix
  describe: trivial style fixes
  transport-helper: trivial style fix
  sha1-name: trivial style cleanup
  branch: trivial style fix
  revision: add missing include
  doc/pull: clarify the illustrations
  t: replace pulls with merges
  merge: simplify ff-only option