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

revision.h

@@ -190,11 +190,11 @@ struct rev_info {
 			show_root_diff:1,
 			no_commit_id:1,
 			verbose_header:1,
-			ignore_merges:1,
 			combine_merges:1,
 			combined_all_paths:1,
 			dense_combined_merges:1,
 			always_show_header:1;
+	int             ignore_merges:2;
 
 	/* Format info */
 	int		show_notes;