Ticket 50659 AddressSanitizer: SEGV ... in bdb_pre_close
    
    Bug: The crash reported is caused by calling dblayer_close twice in some
    	offline exec modes. Investigating the crash revealed another crash
    	in dbverify and memory leaks, one introduced by the backend
    	patch, two existing previously
    
    Fix: 	- call dblayer_close only once
    	- initialize db env properly in dbverify execmode
    	- don't set sdn by reference when adding to entrydncache
    	- free collected instances from commandline in dbupgrade mode
    	- free bdb env in index mode
    
    Reviewed by: William