Bug 139110 GUI enhancement to support create subquery more conveniently.
Description: GUI enhancement to support create subquery more conveniently. Steps to reproduce: Subquery means insert table/list inside another table/list item, and the inner table/list item doesn't has its own dataset binding. In latest build, if you want to creat a subquery structure, you have to use dataSetRow as binding expression for data items in inner table/list item. For example: 1. Insert a list, generate column data binding for it. 2. Add a group for the list. 3. Insert table to list group header which is used to display data rows in list group. Dont' bind table to dataset. 4. Insert a data to table detail row. 5. New a binding column for data, click to Open Expression Builder. The issue is that only "Availabel column bindings" is listed in Category but no "Available Data Sets". So I have to type dataSetRow[".."] by myself to generate correct subquery. For users, maybe they will mistakenly use "Available column bindings" which will generate expression like row._outer[".."] and get wrong result. So it is recommended to add "Available Data Sets" in Expression Builder for such case.
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
return bindingList;
	}
	/**
	 * Returns the element handle which can save binding columns the given
	 * element
	 * 
	 * @param handle
	 *            the handle of the element which needs binding columns
	 * @return the holder for the element,or itself if no holder available
	 */
	public static ReportItemHandle getBindingHolder( DesignElementHandle handle )
	{
		if ( handle instanceof ReportElementHandle )
		{
			if ( handle instanceof ListingHandle )
			{
				return (ReportItemHandle) handle;
			}
			if ( handle instanceof ReportItemHandle )
			{
				if ( ( (ReportItemHandle) handle ).getDataSet( ) != null
						&& ( (ReportItemHandle) handle ).columnBindingsIterator( )
								.hasNext( ) )
				{
					return (ReportItemHandle) handle;
				}
			}
			ReportItemHandle result = getBindingHolder( handle.getContainer( ) );
			if ( result == null && handle instanceof ReportItemHandle )
			{