Bug 145478 Unable "Select Value" in the Join data set's filter
Step to reproduce: 1.new a join data set(please use the attached file) 2.right click the dataset and click the Edit 3.go to the Filter pane and set a filer 4.click the list of Value1 Actual result: A warning pop up and cant select Value.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/data/ui/util/DataSetProvider.java
/**
	 * @param dataSourceType
	 * @return
	 */
	public static IConfigurationElement findDataSourceElement(
			String dataSourceType )
	{
		assert ( dataSourceType != null );
		
		IConfigurationElement element = (IConfigurationElement) htDataSourceExtensions.get( dataSourceType );
		if ( element == null )
		{
			IConfigurationElement[] elements = Platform.getExtensionRegistry( )
					.getConfigurationElementsFor( "org.eclipse.birt.report.designer.ui.odadatasource" ); 			for ( int n = 0; n < elements.length; n++ )
			{
				if ( elements[n].getAttribute( "id" ).equals( dataSourceType ) ) 
				{
					element = elements[n];
					htDataSourceExtensions.put( dataSourceType, element );
					break;
				}
			}
			 elements = Platform.getExtensionRegistry( )
					.getConfigurationElementsFor( "org.eclipse.datatools.connectivity.oda.design.ui.dataSource" ); 			for ( int n = 0; n < elements.length; n++ )
			{
				if ( elements[n].getAttribute( "id" ).equals( dataSourceType ) ) 
				{
					element = elements[n];
					htDataSourceExtensions.put( dataSourceType, element );
					break;