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.

include/timeout.h

@@ -39,6 +39,15 @@ enum timeout_types {
     NUM_TIME_FUNCS
 };
 
+#define timer_is_obj(ttype) ((ttype) == ROT_ORGANIC      \
+                             || (ttype) == ROT_CORPSE    \
+                             || (ttype) == REVIVE_MON    \
+                             || (ttype) == ZOMBIFY_MON   \
+                             || (ttype) == BURN_OBJECT   \
+                             || (ttype) == HATCH_EGG     \
+                             || (ttype) == FIG_TRANSFORM \
+                             || (ttype) == SHRINK_GLOB)
+
 /* used in timeout.c */
 typedef struct fe {
     struct fe *next;          /* next item in chain */