Merge branch 'stable-2.6'

* stable-2.6:
  TrivialRebase: Correctly handle empty patch-id
  TrivialRebase: Support alternative ssh executable
  TrivialRebase: Add server argument
  TrivialRebase: Make private key argument optional
  TrivialRebase: Pipe subprocesses directly
  TrivialRebase: Skip unsupported categories
  TrivialRebase: Raise exception on error
  TrivialRebase: Refactor as a class
  Read initial ack for scp

gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/ScpCommand.java

@@ -92,6 +92,7 @@ final class ScpCommand extends BaseCommand {
 
   private void runImp() {
     try {
+      readAck();
       if (error != null) {
         throw error;
       }