Clear undo stack on rollback. Fixes #2287.

git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@12510 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: wonder

src/core/qgsvectorlayer.cpp

@@ -3414,6 +3414,8 @@ bool QgsVectorLayer::rollBack()
 
   deleteCachedGeometries();
 
+  undoStack()->clear();
+
   mEditable = false;
   emit editingStopped();
 
@@ -3423,7 +3425,6 @@ bool QgsVectorLayer::rollBack()
   setCacheImage( 0 );
   triggerRepaint();
 
-
   return true;
 }