Add CHECK_PLNAME to sysconf

Setting CHECK_PLNAME to 1 makes WIZARDS, EXPLORERS, and SHELLERS
check the player name instead of the user's login name.

This is mostly useful for public servers which have external
login system and don't create user accounts for players.

src/sys.c

@@ -72,6 +72,7 @@ sys_early_init()
 #endif
 
     sysopt.check_save_uid = 1;
+    sysopt.check_plname = 0;
     sysopt.seduce = 1; /* if it's compiled in, default to on */
     sysopt_seduce_set(sysopt.seduce);
     return;