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.tests/test/org/eclipse/birt/data/engine/binding/DataSetCacheTest.java
* Test feature of whether cache will be used
	 * @throws BirtException
	 */
	public void testUseCache1( ) throws BirtException, Exception
	{
		this.dataSet.setCacheRowCount( 100 );
		DataEngineImpl myDataEngine = newDataEngine( );
		assertFalse( getDataSetCacheManager( myDataEngine ).doesLoadFromCache( ) );
		assertFalse( getDataSetCacheManager( myDataEngine ).doesSaveToCache( ) );
		executeQuery(myDataEngine);
	}
	private void executeQuery(DataEngineImpl myDataEngine) throws BirtException, DataException, Exception, IOException {
		QueryDefinition qd = this.newReportQuery( );
		rowBeArray = getRowExpr( );
		totalBeArray = getAggrExpr( );
		bindingNameRow = getRowExprName( );
		bindingExprRow = getAggrExprName( );
		prepareExprNameAndQuery( rowBeArray,
				bindingNameRow,
				totalBeArray,
				bindingExprRow,
				qd );
		IQueryResults qr = myDataEngine.prepare( qd, appContextMap )
				.execute( null );
		qr.getResultIterator( ).next( );
		qr.close( );
		
		String[] bindingNameGroup = new String[1];
		bindingNameGroup[0] = "GROUP_CITY";
		IBaseExpression[] bindingExprGroup = new IBaseExpression[1];