Explicitly the batchMode to true

To prevent a warning about a missing input stream we explicitly set
batchMode when invoking other maven commands

fixes MJAVADOC-537
diff --git a/src/main/java/org/apache/maven/plugins/javadoc/JavadocUtil.java b/src/main/java/org/apache/maven/plugins/javadoc/JavadocUtil.java
index da72cac..ea7e6fb 100644
--- a/src/main/java/org/apache/maven/plugins/javadoc/JavadocUtil.java
+++ b/src/main/java/org/apache/maven/plugins/javadoc/JavadocUtil.java
@@ -920,6 +920,7 @@
         InvocationRequest request = new DefaultInvocationRequest();

         request.setBaseDirectory( projectFile.getParentFile() );

         request.setPomFile( projectFile );

+        request.setBatchMode( true );

         if ( log != null )

         {

             request.setDebug( log.isDebugEnabled() );