Change special keys into extended commands

Changes most of the special keys used in the main input loop
into extended commands:

- movement keys are now bound to extended commands, eg.
  #movewest and so on.

- m-prefix is now #reqmenu extended command, still bound to
  the 'm' key.

- run, rush, and fight are now extended commands, still bound
  to the same keys as previously.

- nopickup and runnopickup keys are removed.
  Nopickup was using 'm' key, the same as the m-prefix, so
  allow #reqmenu to modify movement commands to disable pickup.

- multiple prefix commands are allowed. This lets user to
  use #reqmenu, followed by #run, followed by movement to simulate
  runnopickup behaviour. (If necessary, adding runnopickup back
  as an extended command would be easy)

src/do.c

@@ -1120,6 +1120,8 @@ dodown(void)
     if (trap && Is_stronghold(&u.uz)) {
         goto_hell(FALSE, TRUE);
     } else {
+        if (!trap)
+            u.dz = 1;
         g.at_ladder = (boolean) (levl[u.ux][u.uy].typ == LADDER);
         next_level(!trap);
         g.at_ladder = FALSE;
@@ -1173,6 +1175,7 @@ doup(void)
         return ECMD_OK;
     }
     g.at_ladder = (boolean) (levl[u.ux][u.uy].typ == LADDER);
+    u.dz = -1;
     prev_level(TRUE);
     g.at_ladder = FALSE;
     return ECMD_TIME;
@@ -2046,7 +2049,7 @@ cmd_safety_prevention(const char *cmddesc, const char *act, int *flagcounter)
         buf[0] = '\0';
         if (iflags.cmdassist || !(*flagcounter)++)
             Sprintf(buf, "  Use '%s' prefix to force %s.",
-                    visctrl(g.Cmd.spkeys[NHKF_REQMENU]), cmddesc);
+                    visctrl(cmd_from_func(do_reqmenu)), cmddesc);
         Norep("%s%s", act, buf);
         return TRUE;
     }