Database handles can now be configured to allow exclusive access to the
	database.  To enable exclusive access, call DB->set_lk_exclusive() before
	calling DB->open().  Set nowait_onoff to non-zero to have DB->open() return
	immediately, with the error DB_LOCK_NOTGRANTED if 
	it cannot immediately get exclusive access to the database, and to 
	0 to have DB->open() block until it can gain exclusive access.