Fixed the bug that dataset preview does not work

when script is written for modifying the data set.

Desciption: User has defined a query in the data set. However in
DataSet beforeOpen method they wrote some code in order to replace the sql
query executed by the dataset. The report works well when executed and I
 can see that the dataSet query has been replaced by the query defined
in the DataSet beforeOpen method. However the "preview dataset results"
functionality doesn't work. An exception is raised.

Signed-off-by: Carl Thronson <cthronson@actuate.com>

UI/org.eclipse.birt.report.designer.ui.data/src/org/eclipse/birt/report/designer/data/ui/dataset/ResultSetPreviewPage.java

@@ -431,8 +431,14 @@ private EngineConfig getEngineConfig( ModuleHandle handle )
 			parent = this.getClass( ).getClassLoader( );
 		}
 		ClassLoader customClassLoader = DataSetProvider.getCustomScriptClassLoader( parent, handle );
-		ec.getAppContext( ).put( EngineConstants.APPCONTEXT_CLASSLOADER_KEY,
-				customClassLoader );
+
+//		"customerClassLoader" should not be set into engine appContext, which results in using wrong
+//		classLoader later in JavascriptEvalUtil class. Comment the following lines can make data
+//		preview work correctly.
+
+
+//		ec.getAppContext( ).put( EngineConstants.APPCONTEXT_CLASSLOADER_KEY,
+//				customClassLoader );
 		return ec;
 	}