start of generalizing remotes

Goal is to support multiple different types of remotes, some of which
are not git repositories. To that end, added a Remote class, and moved
git remote specific code into Remote.GitRemote.

Remotes.hs is still present as some code has not been converted to use the
new Remote class yet.

RemoteClass.hs

@@ -0,0 +1,46 @@
+{- git-annex remotes class
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module RemoteClass where
+
+import Control.Exception
+
+import Annex
+import UUID
+import Key
+
+data Remote = Remote {
+	-- each Remote has a unique uuid
+	uuid :: UUID,
+	-- each Remote has a human visible name
+	name :: String,
+	-- Remotes have a use cost; higher is more expensive
+	cost :: Int,
+	-- Transfers a key to the remote.
+	storeKey :: Key -> Annex Bool,
+	-- retrieves a key's contents to a file
+	retrieveKeyFile :: Key -> FilePath -> Annex Bool,
+	-- removes a key's contents
+	removeKey :: Key -> Annex Bool,
+	-- Checks if a key is present in the remote; if the remote
+	-- cannot be accessed returns a Left error.
+	hasKey :: Key -> Annex (Either IOException Bool),
+	-- Some remotes can check hasKey without an expensive network
+	-- operation.
+	hasKeyCheap :: Bool
+}
+
+instance Show Remote where
+	show remote = "Remote { uuid =\"" ++ uuid remote ++ "\" }"
+
+-- two remotes are the same if they have the same uuid
+instance Eq Remote where
+	a == b = uuid a == uuid b
+
+-- order remotes by cost
+instance Ord Remote where
+	compare a b = compare (cost a) (cost b)