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
/**
	 * Returns a handle to the data source for this data set.
	 * 
	 * @return handle to the data source, or <code>null</code> if the data
	 *         source is not set or is undefined.
	 */
	public DataSourceHandle getDataSource( )
	{
		return (DataSourceHandle) getElementProperty( ISimpleDataSetModel.DATA_SOURCE_PROP );
	}
	/**
	 * Returns the name of the data source for this data set.
	 * 
	 * @return the data source name as a string
	 * 
	 * @see #setDataSource(String)
	 */
	public String getDataSourceName( )
	{
		return getStringProperty( ISimpleDataSetModel.DATA_SOURCE_PROP );
	}
	/**
	 * Sets the name of the data source for this data set. This method checks
	 * whether the data source name exists in the report design.
	 * 
	 * @param name
	 *            the data source name
	 * @throws SemanticException
	 *             if the data source does not exist in the report design, or
	 *             the property if locked.