Add sysconf BONES_POOLS to allow more bones-files per level

Reduce the chance of a player playing on a public server encountering
their own bones, by implementing separate bones pools. The pool a player
belongs to is determined at game start, and only bones in that pool
are used. The sysconf BONES_POOLS allows the sysadmin to define how
many pools there are.

include/sys.h

@@ -27,6 +27,7 @@ struct sysopt {
     int seduce;
     int check_save_uid; /* restoring savefile checks UID? */
     int check_plname; /* use plname for checking wizards/explorers/shellers */
+    int bones_pools;
 
     /* record file */
     int persmax;