close window and start process asynchronously;

--- a/src/Pure/System/cygwin_init.scala	Thu Sep 05 21:37:32 2013 +0200
+++ b/src/Pure/System/cygwin_init.scala	Thu Sep 05 22:08:25 2013 +0200
@@ -52,8 +52,11 @@
     {
       _return_code match {
         case None =>
-        case Some(0) => start
-        case Some(rc) => sys.exit(rc)
+        case Some(0) =>
+          visible = false
+          default_thread_pool.submit(() => start)
+        case Some(rc) =>
+          sys.exit(rc)
       }
     }