unused, dropunused: Now work in bare repositories.

Turned out I had already done all the work needed to support this when
unused started checking all branches.

Command/Unused.hs

@@ -36,7 +36,7 @@ seek = [withNothing start]
 
 {- Finds unused content in the annex. -} 
 start :: CommandStart
-start = notBareRepo $ do
+start = do
 	from <- Annex.getState Annex.fromremote
 	let (name, action) = case from of
 		Nothing -> (".", checkUnused)