Flush output every time we write to it in StreamDumper

To try harder to get our errors displayed.

launch/src/main/scala/xsbt/boot/ServerApplication.scala

@@ -101,6 +101,7 @@ class StreamDumper(in: java.io.BufferedReader, out: java.io.PrintStream) extends
       case null => ()
       case line =>
         out.println(line)
+        out.flush()
         read()
     }
     read()