sameas RemoteConfig inheritance

I found a way to avoid inheritance complicating anything outside of
Logs.Remote. It seems fine to require all inherited values to be
inherited and not set in the sameas remote's config. Since inherited
values will be used for stuff like encryption and perhaps chunking, which
control the actual content stored on the remote, it seems likely that
there will not be any reason to need them to vary between two remotes
that access the same underlying data store.

The newer version of containers is free; the minimum ghc version is
bundled with a newer version than that.

Remote/Helper/Encryptable.hs

@@ -29,6 +29,7 @@ import Config
 import Crypto
 import Types.Crypto
 import qualified Annex
+import Annex.SpecialRemote.Config
 
 -- Used to ensure that encryption has been set up before trying to
 -- eg, store creds in the remote config that would need to use the
@@ -55,7 +56,7 @@ encryptionSetup c gc = do
 	maybe (genCipher cmd) (updateCipher cmd) (extractCipher c)
   where
 	-- The type of encryption
-	encryption = M.lookup "encryption" c
+	encryption = M.lookup encryptionField c
 	-- Generate a new cipher, depending on the chosen encryption scheme
 	genCipher cmd = case encryption of
 		_ | hasEncryptionConfig c -> cannotchange
@@ -68,7 +69,7 @@ encryptionSetup c gc = do
 		Just "pubkey" -> encsetup $ genEncryptedCipher cmd (c, gc) key PubKey
 		Just "sharedpubkey" -> encsetup $ genSharedPubKeyCipher cmd key
 		_ -> giveup $ "Specify " ++ intercalate " or "
-			(map ("encryption=" ++)
+			(map ((encryptionField ++ "=") ++)
 				["none","shared","hybrid","pubkey", "sharedpubkey"])
 			++ "."
 	key = fromMaybe (giveup "Specify keyid=...") $ M.lookup "keyid" c
@@ -153,7 +154,7 @@ storeCipher cip = case cip of
 extractCipher :: RemoteConfig -> Maybe StorableCipher
 extractCipher c = case (M.lookup "cipher" c,
 			M.lookup "cipherkeys" c <|> M.lookup "pubkeys" c,
-			M.lookup "encryption" c) of
+			M.lookup encryptionField c) of
 	(Just t, Just ks, encryption) | maybe True (== "hybrid") encryption ->
 		Just $ EncryptedCipher (fromB64bs t) Hybrid (readkeys ks)
 	(Just t, Just ks, Just "pubkey") ->
@@ -167,7 +168,7 @@ extractCipher c = case (M.lookup "cipher" c,
 	readkeys = KeyIds . splitc ','
 
 isEncrypted :: RemoteConfig -> Bool
-isEncrypted c = case M.lookup "encryption" c of
+isEncrypted c = case M.lookup encryptionField c of
 	Just "none" -> False
 	Just _ -> True
 	Nothing -> hasEncryptionConfig c