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
* before opening this data set.
	 * 
	 * @param code
	 *            the code for the method
	 * @throws SemanticException
	 *             If the method is locked.
	 */
	public void setBeforeOpen( String code ) throws SemanticException
	{
		setProperty( ISimpleDataSetModel.BEFORE_OPEN_METHOD, code );
	}
	/**
	 * Returns the code of the beforeClose method. This is the script called
	 * just before closing this data set.
	 * 
	 * @return the code of the method
	 */
	public String getBeforeClose( )
	{
		return getStringProperty( ISimpleDataSetModel.BEFORE_CLOSE_METHOD );
	}
	/**
	 * Sets the code for the beforeClose method. This is the script called just
	 * before closing this data set.
	 * 
	 * @param code
	 *            the code for the method
	 * @throws SemanticException
	 *             If the method is locked.
	 */