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.

Annex/SpecialRemote/Config.hs

@@ -11,6 +11,7 @@ import Common
 import Types.Remote (RemoteConfigField, RemoteConfig)
 
 import qualified Data.Map as M
+import qualified Data.Set as S
 
 {- The name of a configured remote is stored in its config using this key. -}
 nameField :: RemoteConfigField
@@ -35,3 +36,13 @@ typeField = "type"
 autoEnableField :: RemoteConfigField
 autoEnableField = "autoenable"
 
+encryptionField :: RemoteConfigField
+encryptionField = "encryption"
+
+{- A remote with sameas-uuid set will inherit these values from the config
+ - of that uuid. These values cannot be overridden. -}
+sameasInherits :: S.Set RemoteConfigField
+sameasInherits = S.fromList
+	[ encryptionField
+	-- TODO more encryption related fields
+	]