refactor ExportActions

This will allow disabling exports for remotes that are not configured to
allow them. Also, exportSupported will be useful for the external
special remote to probe.

This commit was supported by the NSF-funded DataLad project

Remote/Git.hs

@@ -50,6 +50,7 @@ import Utility.Batch
 import Utility.SimpleProtocol
 import Remote.Helper.Git
 import Remote.Helper.Messages
+import Remote.Helper.Export
 import qualified Remote.Helper.Ssh as Ssh
 import qualified Remote.GCrypt
 import qualified Remote.P2P
@@ -157,11 +158,7 @@ gen r u c gc
 			, lockContent = Just (lockKey new)
 			, checkPresent = inAnnex new
 			, checkPresentCheap = repoCheap r
-			, storeExport = Nothing
-			, retrieveExport = Nothing
-			, removeExport = Nothing
-			, checkPresentExport = Nothing
-			, renameExport = Nothing
+			, exportActions = exportUnsupported
 			, whereisKey = Nothing
 			, remoteFsck = if Git.repoIsUrl r
 				then Nothing