Merge branch 'jc/maint-co-track'

* jc/maint-co-track:
  Enhance hold_lock_file_for_{update,append}() API
  demonstrate breakage of detached checkout with symbolic link HEAD
  Fix "checkout --track -b newbranch" on detached HEAD

Conflicts:
	builtin-commit.c

branch.c

@@ -129,7 +129,9 @@ void create_branch(const char *head,
 			die("Cannot setup tracking information; starting point is not a branch.");
 		break;
 	case 1:
-		/* Unique completion -- good */
+		/* Unique completion -- good, only if it is a real ref */
+		if (track == BRANCH_TRACK_EXPLICIT && !strcmp(real_ref, "HEAD"))
+			die("Cannot setup tracking information; starting point is not a branch.");
 		break;
 	default:
 		die("Ambiguous object name: '%s'.", start_name);