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
return (CachedMetaDataHandle) value.getHandle( propHandle );
	}
	/**
	 * Set the value for the cached data set information.
	 * 
	 * @param metadata
	 *            a structure value include output column information ,
	 *            input/output parameter definitions.
	 * @return <code>CachedMetaDataHandle</code> to the input
	 *         <code>metadata</code>, return <code>null</code> if
	 *         <code>metadata</code> is <code>null</code>.
	 * @throws SemanticException
	 *             the input data is not valid.
	 */
	public CachedMetaDataHandle setCachedMetaData( CachedMetaData metadata )
			throws SemanticException
	{
		setProperty( CACHED_METADATA_PROP, metadata );
		if ( metadata == null )
			return null;
		return (CachedMetaDataHandle) metadata
				.getHandle( getPropertyHandle( CACHED_METADATA_PROP ) );
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.api.DesignElementHandle#getPropertyHandle(java.lang.String)
	 */
	public PropertyHandle getPropertyHandle( String propName )
	{