Make -f set -a, as required by the standard.

From the original OpenBSD commit message:

  restore the traditional behavior of -f implying -a; apparently Keith
  Bostic forgot to restore it when the -f flag was put back on 2nd of
  September 1989, after being removed on 16th of August as a
  consequence of issues getting it working over NFS, so deviation from
  traditional UNIX behavior in all BSDs looks like an historical
  accident; as a side effect, this change accommodates behavior of
  this option to IEEE Std 1003.1-2008 (``POSIX.1'').

  joint work with jmc@ (who found the inaccuracy in our
  implementation), schwarze@ (who provided a detailed tracking of
  historical facts) and millert@

Submitted by: Igor Sobrado
Discussed with:  mckusick
Obtained from: OpenBSD project
MFC after:  2 weeks

bin/ls/ls.1

@@ -194,6 +194,8 @@ Use time when file status was last changed for sorting or printing.
 Directories are listed as plain files (not searched recursively).
 .It Fl f
 Output is not sorted.
+This option turns on
+.Fl a .
 .It Fl g
 This option is deprecated and is only available for compatibility
 with

bin/ls/ls.c

@@ -226,6 +226,9 @@ main(int argc, char *argv[])
 			f_accesstime = 0;
 			f_statustime = 0;
 			break;
+		case 'f':
+			f_nosort = 1;
+		       /* FALLTHROUGH */
 		case 'a':
 			fts_options |= FTS_SEEDOT;
 			/* FALLTHROUGH */
@@ -300,9 +303,6 @@ main(int argc, char *argv[])
 			f_listdir = 1;
 			f_recursive = 0;
 			break;
-		case 'f':
-			f_nosort = 1;
-			break;
 		case 'g':	/* Compatibility with 4.3BSD. */
 			break;
 		case 'h':