Added support for 64bit ticks (#3768)

Fixes #3017

Thanks to Hercules for the idea and their implementation of it.

This deprecates Windows XP support. If you want to use it to run your server on it, you have to forcefully enable it now.
Since 64bit ticks do not exist on XP, you might encounter some issues that are already fixed on other OS.

src/map/mercenary.cpp

@@ -106,7 +106,7 @@ bool mercenary_create(struct map_session_data *sd, uint16 class_, unsigned int l
 * @param md The Mercenary
 * @return The Lifetime
 **/
-int mercenary_get_lifetime(struct mercenary_data *md) {
+t_tick mercenary_get_lifetime(struct mercenary_data *md) {
 	const struct TimerData * td;
 	if( md == NULL || md->contract_timer == INVALID_TIMER )
 		return 0;