be stricter about rejecting invalid configurations for remotes

This is a first step toward that goal, using the ProposedAccepted type
in RemoteConfig lets initremote/enableremote reject bad parameters that
were passed in a remote's configuration, while avoiding enableremote
rejecting bad parameters that have already been stored in remote.log

This does not eliminate every place where a remote config is parsed and a
default value is used if the parse false. But, I did fix several
things that expected foo=yes/no and so confusingly accepted foo=true but
treated it like foo=no. There are still some fields that are parsed with
yesNo but not not checked when initializing a remote, and there are other
fields that are parsed in other ways and not checked when initializing a
remote.

This also lays groundwork for rejecting unknown/typoed config keys.

Annex/FileMatcher.hs

@@ -39,6 +39,7 @@ import Types.GitConfig
 import Config.GitConfig
 import Git.FilePath
 import Types.Remote (RemoteConfig)
+import Types.ProposedAccepted
 import Annex.CheckAttr
 import Git.CheckAttr (unspecifiedAttr)
 import qualified Git.Config
@@ -155,8 +156,8 @@ preferredContentKeylessTokens pcd =
 	, SimpleToken "inpreferreddir" (simply $ limitInDir preferreddir)
 	] ++ commonKeylessTokens LimitAnnexFiles
   where
-	preferreddir = fromMaybe "public" $
-		M.lookup "preferreddir" =<< (`M.lookup` configMap pcd) =<< repoUUID pcd
+	preferreddir = maybe "public" fromProposedAccepted $
+		M.lookup (Accepted "preferreddir") =<< (`M.lookup` configMap pcd) =<< repoUUID pcd
 
 preferredContentKeyedTokens :: PreferredContentData -> [ParseToken (MatchFiles Annex)]
 preferredContentKeyedTokens pcd =