experimental config option TTY_PERM_INVENT

Add a rudimentary experimental always-up inventory display
capability to tty when the perm_invent option is in effect.
It requires an additional 28 rows available on the terminal
underneath the bottom status line.

It hasn't been optimized for performance as of yet.

src/display.c

@@ -1507,9 +1507,11 @@ docrt(void)
     register int x, y;
     register struct rm *lev;
 
-    if (!u.ux)
+    if (!u.ux || g.program_state.in_docrt)
         return; /* display isn't ready yet */
 
+    g.program_state.in_docrt = TRUE;
+
     if (u.uswallow) {
         swallowed(1);
         goto post_map;
@@ -1552,6 +1554,7 @@ docrt(void)
     update_inventory();
 
     g.context.botlx = 1; /* force a redraw of the bottom line */
+    g.program_state.in_docrt = FALSE;
 }
 
 /* for panning beyond a clipped region; resend the current map data to