filer: add leveldb3

support dedicated leveldb instance for each bucket

weed/command/scaffold.go

@@ -89,6 +89,12 @@ buckets_folder = "/buckets"
 enabled = true
 dir = "./filerldb2"					# directory to store level db files
 
+[leveldb3]
+# similar to leveldb2.
+# each bucket has its own meta store.
+enabled = false
+dir = "./filerldb3"					# directory to store level db files
+
 [rocksdb]
 # local on disk, similar to leveldb
 # since it is using a C wrapper, you need to install rocksdb and build it by yourself