menuconfig: Add Save/Load buttons

If menuconfig have Save/Load button like alternative
.config editors, xconfig, nconfig, etc.We will have
a obvious benefit when use menuconfig just like
when we use others, we can Save/Load our .config quickly
and conveniently.

This patch add the Save/Load button for menuconfig.

[remove trailing space while at it for below line:
"*)  Formerly when I used Page Down and Page Up, the cursor would be set"
]

Changes:
V1-V2:
1:use PATH_MAX instead of hard code suggested by Yann E. MORIN
2:drop the spurious empty-line removal suggested by Yann E. MORIN
V2-V3:
1:ajust buttons position well centered reported by Yann E. MORIN

Signed-off-by: Wang YanQing <udknight@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
diff --git a/scripts/kconfig/mconf.c b/scripts/kconfig/mconf.c
index 5f29618..88e80685 100644
--- a/scripts/kconfig/mconf.c
+++ b/scripts/kconfig/mconf.c
@@ -280,6 +280,7 @@
 static int child_count;
 static int single_menu_mode;
 static int show_all_options;
+static int save_and_exit;
 
 static void conf(struct menu *menu, struct menu *active_menu);
 static void conf_choice(struct menu *menu);
@@ -657,6 +658,12 @@
 				show_helptext(_("README"), _(mconf_readme));
 			break;
 		case 3:
+			conf_save();
+			break;
+		case 4:
+			conf_load();
+			break;
+		case 5:
 			if (item_is_tag('t')) {
 				if (sym_set_tristate_value(sym, yes))
 					break;
@@ -664,24 +671,24 @@
 					show_textbox(NULL, setmod_text, 6, 74);
 			}
 			break;
-		case 4:
+		case 6:
 			if (item_is_tag('t'))
 				sym_set_tristate_value(sym, no);
 			break;
-		case 5:
+		case 7:
 			if (item_is_tag('t'))
 				sym_set_tristate_value(sym, mod);
 			break;
-		case 6:
+		case 8:
 			if (item_is_tag('t'))
 				sym_toggle_tristate_value(sym);
 			else if (item_is_tag('m'))
 				conf(submenu, NULL);
 			break;
-		case 7:
+		case 9:
 			search_conf();
 			break;
-		case 8:
+		case 10:
 			show_all_options = !show_all_options;
 			break;
 		}
@@ -708,6 +715,17 @@
 	show_textbox(title, text, 0, 0);
 }
 
+static void conf_message_callback(const char *fmt, va_list ap)
+{
+	char buf[PATH_MAX+1];
+
+	vsnprintf(buf, sizeof(buf), fmt, ap);
+	if (save_and_exit)
+		printf("%s", buf);
+	else
+		show_textbox(NULL, buf, 6, 60);
+}
+
 static void show_help(struct menu *menu)
 {
 	struct gstr help = str_new();
@@ -876,6 +894,7 @@
 {
 	int res;
 
+	save_and_exit = 1;
 	dialog_clear();
 	if (conf_get_changed())
 		res = dialog_yesno(NULL,
@@ -947,6 +966,7 @@
 	}
 
 	set_config_filename(conf_get_configname());
+	conf_set_message_callback(conf_message_callback);
 	do {
 		conf(&rootmenu, NULL);
 		res = handle_exit();