Lua: object timers

Expose object timers to lua scripts. For example:

   local o = obj.new("cockatrice egg");
   o:placeobj(5, 5);
   o:start_timer("hatch-egg", 3);

Available methods are:

- obj.has_timer("rot-corpse")
    returns true if object has attached timer, false otherwise.

- obj.peek_timer("hatch-egg")
    returns an integer value, which is the turn when the timer
    attached to the object would trigger. returns 0 if no such timer.

- obj.stop_timer("shrink-glob")
    stops attached timer, or if no timer type is given, stops all
    timers attached to the object.

- obj.start_timer("zombify-mon", 15)
    starts a timer with a trigger time in that many turns in the future.
    replaces any previous timer of the same type.

Valid timers are "rot-organic", "rot-corpse", "revive-mon",
"zombify-mon", "burn-obj", "hatch-egg", "fig-transform",
and "shrink-glob". Also "melt-ice" is recognized, but does nothing
to objects.

src/nhlua.c

@@ -191,6 +191,21 @@ get_table_mapchr_opt(lua_State *L, const char *name, schar defval)
     return typ;
 }
 
+short
+nhl_get_timertype(lua_State *L, int idx)
+{
+    static const char *const timerstr[NUM_TIME_FUNCS+1] = {
+        "rot-organic", "rot-corpse", "revive-mon", "zombify-mon",
+        "burn-obj", "hatch-egg", "fig-transform", "melt-ice", "shrink-glob",
+        NULL
+    };
+    short ret = luaL_checkoption(L, idx, NULL, timerstr);
+
+    if (ret < 0 || ret >= NUM_TIME_FUNCS)
+        nhl_error(L, "Unknown timer type");
+    return ret;
+}
+
 void
 nhl_add_table_entry_int(lua_State *L, const char *name, int value)
 {