fix up Read instance incompatability caused by recent commit

9c4650358c changed the Read instance for
Key.

I've checked all uses of that instance (by removing it and seeing what
breaks), and they're all limited to the webapp, except one.
That is GitAnnexDistribution's Read instance.

So, 9c4650358c would have broken upgrades
of git-annex from downloads.kitenet.net. Once the .info files there got
updated for a new release, old releases would have failed to parse them
and never upgraded.

To fix this, I found a way to make the .info files that contain
GitAnnexDistribution values be readable by the old version of git-annex.

This commit was sponsored by Ewen McNeill.

Types/Transfer.hs

@@ -16,8 +16,7 @@ import Control.Concurrent
 import Control.Applicative
 import Prelude
 
-{- Enough information to uniquely identify a transfer, used as the filename
- - of the transfer information file. -}
+{- Enough information to uniquely identify a transfer. -}
 data Transfer = Transfer
 	{ transferDirection :: Direction
 	, transferUUID :: UUID
@@ -46,7 +45,16 @@ stubTransferInfo :: TransferInfo
 stubTransferInfo = TransferInfo Nothing Nothing Nothing Nothing Nothing Nothing False
 
 data Direction = Upload | Download
-	deriving (Eq, Ord, Read, Show)
+	deriving (Eq, Ord, Show, Read)
+
+formatDirection :: Direction -> String
+formatDirection Upload = "upload"
+formatDirection Download = "download"
+
+parseDirection :: String -> Maybe Direction
+parseDirection "upload" = Just Upload
+parseDirection "download" = Just Download
+parseDirection _ = Nothing
 
 instance Arbitrary TransferInfo where
 	arbitrary = TransferInfo