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/src/org/eclipse/birt/data/engine/impl/ServiceForQueryResults.java
{
	private DataEngineContext 			context;
	private IPreparedQueryService       queryService;
	private IQueryExecutor				queryExecutor;
	private PreparedDataSourceQuery 	reportQuery;
	private IBaseQueryDefinition 		queryDefn;
	
	private ExprManager					exprManager;
	
	private Scriptable 					scope;
	private int 						nestedLevel;
	
	/**
	 * @param reportQuery
	 * @param query
	 */
	public ServiceForQueryResults( DataEngineContext context, Scriptable scope,
			int nestedLevel, PreparedDataSourceQuery reportQuery,
			IPreparedQueryService query, QueryExecutor queryExecutor,
			IBaseQueryDefinition queryDefn, ExprManager exprManager )
	{
		assert reportQuery != null && queryExecutor != null;
		this.context = context;
		this.scope = scope;
		this.nestedLevel = nestedLevel;
		this.reportQuery = reportQuery;
		this.queryService = query;