cache the trustmap

Doubles the speed of fsck, and speeds up drop as well.

Types/TrustLevel.hs

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+{- git-annex trust levels
+ -
+ - Copyright 2010 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Types.TrustLevel (
+	TrustLevel(..),
+	TrustMap
+) where
+
+import qualified Data.Map as M
+
+import Types.UUID
+
+data TrustLevel = SemiTrusted | UnTrusted | Trusted
+	deriving Eq
+
+instance Show TrustLevel where
+        show SemiTrusted = "?"
+        show UnTrusted = "0"
+        show Trusted = "1"
+
+instance Read TrustLevel where
+        readsPrec _ "1" = [(Trusted, "")]
+        readsPrec _ "0" = [(UnTrusted, "")]
+	readsPrec _ _ = [(SemiTrusted, "")]
+
+type TrustMap = M.Map UUID TrustLevel