fix github issue #499 - perm_invent menu_headings

Implementation of '|'/#perminv command for scrolling perm_invent
deliberately disabled menu_headings (video attribute for object
class separator lines) on the persistent inventory window under
curses.  I don't recall why (possibly because it isn't actually
a menu) but there's no compelling need to do that, so reinstate
heading attributes.

Fixes #499

win/curses/cursinvt.c

@@ -296,7 +296,8 @@ curs_add_invt(
     }
 
     newelement.invtxt = dupstr(str);
-    newelement.c_attr = attr ? A_NORMAL : NONE; /* override menu_headings */
+    newelement.c_attr = attr; /* note: caller has already converted 'attr'
+                               * from tty-style attribute to curses one */
     newelement.letter = accelerator;
     aptr[pi.inuseindx++] = newelement;