allow persistent menu selections

menuselectionpersistent
  Enables persistent selections for the currently displayed menu and also
  restores a previously saved selection. Probably most efficient inside
  "menuinit". The position is restored during execution of this command,
  so the menu entry has to already exist and the alias with the last
  position has to be read from saved.cfg. In autmatically created menus
  it may be necessary to execute the command with a short delay (see
  examples in this commit).

DOCREF menuselectionpersistent

source/src/menus.cpp

@@ -133,6 +133,13 @@ void showmenu_(const char *name)
 }
 COMMANDN(showmenu, showmenu_, "s");
 
+const char *persistentmenuselectionalias(const char *name)
+{
+    static defformatstring(al)("__lastmenusel_%s", name);
+    filtertext(al, al, FTXT__ALIAS);
+    return al;
+}
+
 void menuselect(void *menu, int sel)
 {
     gmenu &m = *(gmenu *)menu;
@@ -151,6 +158,11 @@ void menuselect(void *menu, int sel)
                 if(m.items.inrange(oldsel)) m.items[oldsel]->focus(false);
                 m.items[sel]->focus(true);
                 audiomgr.playsound(S_MENUSELECT, SP_HIGHEST);
+                if(m.persistentselection)
+                {
+                    defformatstring(val)("%d", sel);
+                    alias(persistentmenuselectionalias(m.name), val);
+                }
             }
         }
     }
@@ -886,6 +898,15 @@ void menuinitselection(int *line)
 }
 COMMAND(menuinitselection, "i");
 
+void menuselectionpersistent()
+{
+    if(!curmenu) return;
+    curmenu->persistentselection = true;
+    const char *val = getalias(persistentmenuselectionalias(curmenu->name));
+    if(val) menuselect(curmenu, ATOI(val));
+}
+COMMAND(menuselectionpersistent, "");
+
 void menurenderoffset(int *xoff, int *yoff)
 {
     if(!lastmenu) return;