Merge branch 'jk/log-fp-implies-m'

Merge branch 'jk/log-fp-implies-m'

"git log --first-parent -p" showed patches only for single-parent
commits on the first-parent chain; the "--first-parent" option has
been made to imply "-m".  Use "--no-diff-merges" to restore the
previous behaviour to omit patches for merge commits.

* jk/log-fp-implies-m:
  doc/git-log: clarify handling of merge commit diffs
  doc/git-log: move "-t" into diff-options list
  doc/git-log: drop "-r" diff option
  doc/git-log: move "Diff Formatting" from rev-list-options
  log: enable "-m" automatically with "--first-parent"
  revision: add "--no-diff-merges" option to counteract "-m"
  log: drop "--cc implies -m" logic