Method SetCustomKey

cmn/objmeta.go:80–80

(k, v string)

		GetCustomMD() cos.SimpleKVs
		GetCustomKey(key string) (val string, exists bool)
		SetCustomKey(k, v string)
		String() string
	}
	// see also apc.HdrObjAtime et al. @ api/apc/const.go (and note that naming must be consistent)