curses: digit as menu selector

Menus in the curses interface would honor a digit as a selector
character ("letter" :-) for PICK_ANY menus but forced it to start a
count in PICK_ONE menus.  This fixes that, although the menu where I
was using digits as selectors (not included) has been changed to use
letters so this fix isn't being exercised anymore.

Also, add a couple of comments about persistent inventory.

win/curses/cursdial.c

@@ -1538,7 +1538,8 @@ menu_get_selections(WINDOW *win, nhmenu *menu, int how)
             }
             /*FALLTHRU*/
         default:
-            if (isdigit(curletter) && !groupaccels[curletter]) {
+            if (isdigit(curletter) && !selectors[curletter]
+                && !groupaccels[curletter]) {
                 count = curses_get_count(curletter);
                 /* after count, we know some non-digit is already pending */
                 curletter = curses_getch();