Bug 180842 Config memory buffer size in data engine execution.
To tuning the performance, it is necessary for DtE to expose API for clients to config the size of memory it used to store the final result set. A new AppContext string, "org.eclipse.birt.data.cache.memory.size" is proposed. The new appcontext entry only accept positive integer as input, the unit of which would be MB.
data/org.eclipse.birt.data.tests/test/org/eclipse/birt/data/engine/binding/NestedQueryTest.java
/**
	 * The inner query with a filter row["CustomerID"] equals row._outer["ROW_CUSTOMERID"]
	 * 
	 * @throws Exception
	 */
	public void test5( ) throws Exception
	{
		queryDefnCustomer = createCustomerQueryDefn();
		datasetCall = newDataSet("data set calls", " SELECT * FROM "
				+ callsTableName);
		queryDefnCall = createCallQueryDefn( );
		String[] bindingNameFilter = new String[1];
		bindingNameFilter[0] = "FILTER_CUSTOMERID";
		IBaseExpression[] bindingExprFilter = new IBaseExpression[1];
		bindingExprFilter[0] = new ScriptExpression( "dataSetRow.CU" );
		FilterDefinition filterDefn = new FilterDefinition( new ConditionalExpression( "row._outer[\"ROW_CUSTOMERID\"]",
				ConditionalExpression.OP_EQ,"2"
				 ) );
		FilterDefinition filterDefn1 = new FilterDefinition( new ConditionalExpression( "row[\"ROW_CUSTOMERID\"]",
				ConditionalExpression.OP_EQ,"row._outer[\"ROW_CUSTOMERID\"]"
				 ) );
		
		
		queryDefnCall.addFilter( filterDefn );
		queryDefnCall.addFilter( filterDefn1 );
		
		runNestedQuery();
	}
	
	/**