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
{
	private static DataSetProvider instance = null;
	
	private transient Hashtable htColumns = new Hashtable( 10 );
	private static Hashtable htDataSourceExtensions = new Hashtable( 10 );
	private transient Hashtable sessionTable = new Hashtable( 10 );
	
	private static final char RENAME_SEPARATOR = '_';
	private static String UNNAME_PREFIX = "UNNAMED";