stat_tracking_info(): only count real commits

stat_tracking_info() in remote.c is used to collect the statistics to
be able to say (for instance) from the output of "git checkout':

  Your branch and 'foo' have diverged,
  and have X and Y different commit(s) each, respectively.

Currently X and Y also includes the count of merges.  This patch
excludes the merges from being counted.

Signed-off-by: Kjetil Barvik <barvik@broadpark.no>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.c

@@ -1310,9 +1310,10 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 	if (theirs == ours)
 		return 0;
 
-	/* Run "rev-list --left-right ours...theirs" internally... */
+	/* Run "rev-list --no-merges --left-right ours...theirs" internally... */
 	rev_argc = 0;
 	rev_argv[rev_argc++] = NULL;
+	rev_argv[rev_argc++] = "--no-merges";
 	rev_argv[rev_argc++] = "--left-right";
 	rev_argv[rev_argc++] = symmetric;
 	rev_argv[rev_argc++] = "--";