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.

sys/unix/sysconf

@@ -98,6 +98,14 @@ MAXPLAYERS=10
 #   %N first character of player name
 #DUMPLOGFILE=/tmp/nethack.%n.%d.log
 
+# Number of bones file pools.
+# The pool you belong to is determined at game start. You will
+# load and save bones only from that pool. Generally useful
+# for public servers only.
+# Changing this might make existing bones inaccessible.
+# Disabled by setting to 0, or commenting out.
+#BONES_POOLS=10
+
 # Try to get more info in case of a program bug or crash.  Only used
 # if the program is built with the PANICTRACE compile-time option enabled.
 # By default PANICTRACE is enabled if BETA is defined, otherwise disabled.