Index: /trunk/src/org/openstreetmap/josm/data/osm/DataSet.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/osm/DataSet.java	(revision 5121)
+++ /trunk/src/org/openstreetmap/josm/data/osm/DataSet.java	(revision 5122)
@@ -37,4 +37,5 @@
 import org.openstreetmap.josm.data.projection.Projection;
 import org.openstreetmap.josm.data.projection.ProjectionChangeListener;
+import org.openstreetmap.josm.gui.progress.ProgressMonitor;
 import org.openstreetmap.josm.gui.tagging.ac.AutoCompletionManager;
 import org.openstreetmap.josm.tools.FilteredCollection;
@@ -1166,6 +1167,14 @@
      */
     public void mergeFrom(DataSet from) {
+    	mergeFrom(from, null);
+    }
+    
+    /**
+     * Moves all primitives and datasources from DataSet "from" to this DataSet
+     * @param from The source DataSet
+     */
+    public void mergeFrom(DataSet from, ProgressMonitor progressMonitor) {
         if (from != null) {
-            new DataSetMerger(this, from).merge();
+            new DataSetMerger(this, from).merge(progressMonitor);
             dataSources.addAll(from.dataSources);
             from.dataSources.clear();