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/elements/interfaces/IDataSetModel.java
* The property name of the structures of the expected result set's hint.
	 */
	public static final String RESULT_SET_HINTS_PROP = "resultSetHints"; 
	/**
	 * The property name of the columns computed with expression.
	 */
	public static final String COMPUTED_COLUMNS_PROP = "computedColumns"; 
	/**
	 * The property name of the column hint elements.
	 */
	public static final String COLUMN_HINTS_PROP = "columnHints"; 
	/**
	 * The property name of the filters to apply to the data set.
	 */
	public static final String FILTER_PROP = "filter"; 
	/**
	 * The property name of the data set parameters definitions.
	 */
	public static final String PARAMETERS_PROP = "parameters"; 
	/**
	 * The property name of the cached data set information.
	 */
	public static final String CACHED_METADATA_PROP = "cachedMetaData"; 
	
	/**
	 * The property name of the max number of rows to fetch from data set.
	 */
	public static final String ROW_FETCH_LIMIT_PROP = "rowFetchLimit"; 
}