Fuse update wait thread and update thread:

(update_main): No longer a thread entry point.  Remove the parameter.
Remove *player setup.  Don't terminate the thread when done.
(update_pending): Move to src/server/update.c.
(update_wait): Call update_main() instead of running it in its own
thread.  Set up *player for it.
(update_init): Create the fused update thread instead of the update
wait thread.

include/server.h

@@ -50,7 +50,7 @@ void delete_lostitems(void *);
 void market_update(void *);
 void mobility_check(void *);
 void player_kill_idle(void *);
-void update_main(void *);
+void update_main(void);
 void update_init(void);
 void shutdown_sequence(void *);
 void update_force(void *);