convert configParser to Annex action and add passthrough option

Needed so Remote.External can query the external program for its
configs. When the external program does not support the query,
the passthrough option will make all input fields be available.

Remote/GCrypt.hs

@@ -66,7 +66,8 @@ remote = specialRemoteType $ RemoteType
 	-- and will call our gen on them.
 	, enumerate = const (return [])
 	, generate = gen
-	, configParser = [optionalStringParser gitRepoField]
+	, configParser = mkRemoteConfigParser
+		[optionalStringParser gitRepoField]
 	, setup = gCryptSetup
 	, exportSupported = exportUnsupported
 	, importSupported = importUnsupported
@@ -104,8 +105,9 @@ gen baser u c gc rs = do
 		v <- M.lookup u' <$> readRemoteLog
 		case (Git.remoteName baser, v) of
 			(Just remotename, Just c') -> do
-				pc <- either giveup return $
-					parseRemoteConfig c' (configParser remote)
+				pc <- either giveup return
+					. parseRemoteConfig c'
+					=<< configParser remote
 				setGcryptEncryption pc remotename
 				storeUUIDIn (remoteConfig baser "uuid") u'
 				setConfig (Git.GCrypt.remoteConfigKey "gcrypt-id" remotename) gcryptid
@@ -214,8 +216,8 @@ gCryptSetup _ mu _ c gc = go $ fromProposedAccepted <$> M.lookup gitRepoField c
 				| Git.repoLocation r == url -> noop
 				| otherwise -> error "Another remote with the same name already exists."		
 
-		pc <- either giveup return $
-			parseRemoteConfig c' (configParser remote)
+		pc <- either giveup return . parseRemoteConfig c'
+			=<< configParser remote
 		setGcryptEncryption pc remotename
 
 		{- Run a git fetch and a push to the git repo in order to get