Added mmap support for MyISAM engine


configure.in:
  Added mmap support for MyISAM engine
include/my_base.h:
  Added mmap support for MyISAM engine
include/my_sys.h:
  Added mmap support for MyISAM engine
sql/ha_myisam.cc:
  Added mmap support for MyISAM engine
sql/mysql_priv.h:
  Added mmap support for MyISAM engine
sql/mysqld.cc:
  Added mmap support for MyISAM engine
sql/records.cc:
  Added mmap support for MyISAM engine
sql/set_var.cc:
  Added mmap support for MyISAM engine
storage/myisam/mi_close.c:
  Added mmap support for MyISAM engine
storage/myisam/mi_delete_all.c:
  Added mmap support for MyISAM engine
storage/myisam/mi_dynrec.c:
  Added mmap support for MyISAM engine
storage/myisam/mi_extra.c:
  Added mmap support for MyISAM engine
storage/myisam/mi_locking.c:
  Added mmap support for MyISAM engine
storage/myisam/mi_open.c:
  Added mmap support for MyISAM engine
storage/myisam/mi_packrec.c:
  Added mmap support for MyISAM engine
storage/myisam/mi_statrec.c:
  Added mmap support for MyISAM engine
storage/myisam/myisamdef.h:
  Added mmap support for MyISAM engine