Bug 180189 Support in memory data set cache.
Currently, Design-Time Data Cache is stored on disks. By performance tests using ramdisk, we found that caching in physical memory can improve the performance of RunAndRender by 30%.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/PreparedJointDataSourceQuery.java
* 
	 * @param dataEngine
	 * @param dataSetDesignName
	 * @param appContext
	 * @param joinConditions
	 * @param isLeftDataSet
	 * @return
	 * @throws DataException
	 */
	private IQueryResults getResultSetQuery( DataEngineImpl dataEngine,
			String dataSetDesignName, Map appContext, List joinConditions,
			boolean isLeftDataSet ) throws DataException
	{
		QueryDefinition queryDefinition = new QueryDefinition( );
		
		queryDefinition.setDataSetName( dataSetDesignName );
		setParameterBindings( dataEngine, dataSetDesignName, isLeftDataSet, queryDefinition );
		
		IPreparedQuery preparedQuery;
		try
		{
			preparedQuery = PreparedQueryUtil.newInstance( dataEngine,
					queryDefinition,
					appContext );
			IQueryResults ri = preparedQuery.execute( null );
			
			return ri;
		}
		catch ( BirtException e )
		{