Improve cached content header of status output

This tries to be more to the point while also including a pointer on how to
unstage changes from the index.

Since this header is printed in two different code paths and the name of the
reference commit is needed for the unstage part, provide a new printing
function.

Signed-off-by: Jürgen Rühle <j-r@online.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

wt-status.c

@@ -53,6 +53,18 @@ void wt_status_prepare(struct wt_status *s)
 	s->workdir_clean = 1;
 }
 
+static void wt_status_print_cached_header(const char *reference)
+{
+	const char *c = color(WT_STATUS_HEADER);
+	color_printf_ln(c, "# Cached changes to be committed:");
+	if (reference) {
+		color_printf_ln(c, "#   (use \"git reset %s <file>...\" and \"git rm --cached <file>...\" to unstage)", reference);
+	} else {
+		color_printf_ln(c, "#   (use \"git rm --cached <file>...\" to unstage)");
+	}
+	color_printf_ln(c, "#");
+}
+
 static void wt_status_print_header(const char *main, const char *sub)
 {
 	const char *c = color(WT_STATUS_HEADER);
@@ -147,8 +159,7 @@ static void wt_status_print_updated_cb(struct diff_queue_struct *q,
 		if (q->queue[i]->status == 'U')
 			continue;
 		if (!shown_header) {
-			wt_status_print_header("Added but not yet committed",
-					"will commit");
+			wt_status_print_cached_header(s->reference);
 			s->commitable = 1;
 			shown_header = 1;
 		}
@@ -182,8 +193,7 @@ void wt_status_print_initial(struct wt_status *s)
 	read_cache();
 	if (active_nr) {
 		s->commitable = 1;
-		wt_status_print_header("Added but not yet committed",
-				"will commit");
+		wt_status_print_cached_header(NULL);
 	}
 	for (i = 0; i < active_nr; i++) {
 		color_printf(color(WT_STATUS_HEADER), "#\t");