enable forwardRetry for command-line transfers

If a transfer fails for some reason, but some data managed to be sent, the
transfer will be retried. (The assistant already did this.)

Possible impacts:

* More ssh prompts if ssh needs to prompt for a password to connect to a
  host, or is prompting about some other problem like a ssh key mismatch.

* More data transfer due to retrying, epecially when a remote does not
  support resuming a transfer.

  In the worst case, a lot of data will be transferred but it fails before
  the end, and then all that data gets transferred again plus one byte more;
  repeat until it manages to get the whole file.

Command/SendKey.hs

@@ -48,6 +48,7 @@ fieldTransfer direction key a = do
 	liftIO $ debugM "fieldTransfer" "transfer start"
 	afile <- Fields.getField Fields.associatedFile
 	ok <- maybe (a $ const noop)
+		-- Using noRetry here because we're the sender.
 		(\u -> runner (Transfer direction (toUUID u) key) afile noRetry a)
 		=<< Fields.getField Fields.remoteUUID
 	liftIO $ debugM "fieldTransfer" "transfer done"