more efficient data type for ChangeChan

Making this a tset of lists of Changes, rather than a tset of Changes
makes refilling it, in batch mode, much more efficient. Rather than needing
to add every Change it's collected one at a time, it can add them in one
fast batch operation.

It would be more efficient yet to use a Set, but that would need an Eq
instance for InodeCache.

Assistant/Types/Changes.hs

@@ -22,7 +22,7 @@ changeInfoKey (AddKeyChange k) = Just k
 changeInfoKey (LinkChange (Just k)) = Just k
 changeInfoKey _ = Nothing
 
-type ChangeChan = TSet Change
+type ChangeChan = TSet [Change]
 
 newChangeChan :: IO ChangeChan
 newChangeChan = atomically newTSet