Bug 213126 Add support for DataEngine-leve dataset cache
In many cases the DataEngine-leve dataset cache is useful which ensure that a dataset is executed one time during rendering one report. To support this feature a new dataset property should be added. The Birt customer can choose whether this dataset need to be cached or not by setting the property in deisgn time.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/DataSetHandle.java
{
		PropertyHandle propHandle = getPropertyHandle( ISimpleDataSetModel.PARAM_BINDINGS_PROP );
		assert propHandle != null;
		return propHandle.iterator( );
	}
	/**
	 * Returns an iterator over the result set columns. The iterator returns
	 * instances of <code>ResultSetColumnHandle</code> that represents result
	 * set column object.
	 * 
	 * @return iterator over result set columns.
	 * 
	 * @see org.eclipse.birt.report.model.api.elements.structures.ResultSetColumn
	 */
	public Iterator resultSetIterator( )
	{
		PropertyHandle propHandle = getPropertyHandle( RESULT_SET_PROP );
		assert propHandle != null;
		return propHandle.iterator( );
	}
	/**
	 * Returns an iterator over hints of the result set columns. The iterator
	 * returns instances of <code>ResultSetColumnHandle</code> that represents
	 * hints of result set column object.
	 * 
	 * @return iterator over hints of result set columns.
	 * 
	 * @see org.eclipse.birt.report.model.api.elements.structures.ResultSetColumn
	 */
	public Iterator resultSetHintsIterator( )