add Annex worker pool to P2PHttp

This will be needed for get and store, since those need to run Annex
actions.

withLocalP2PConnections will also probably use it.

P2P/Protocol.hs

@@ -49,7 +49,7 @@ import Control.DeepSeq
 import Prelude
 
 newtype Offset = Offset Integer
-	deriving (Show, NFData)
+	deriving (Show, Eq, NFData, Num, Real, Ord, Enum, Integral)
 
 newtype Len = Len Integer
 	deriving (Show)