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/api/APITestCase.java
{
		return Util.instance.getDefaultQueryDefnWithSubQuery( dataSetName );
	}
	
	/**
	 * Return expression of default query
	 * @return expression of default query
	 */
	protected BaseExpression[] getExpressionsOfDefaultQuery( )
	{
		return Util.instance.getExpressionsOfDefaultQuery( );
	}
	
	protected String[] getBindingExpressionName( )
	{
		return Util.instance.getBindingExpressionName( );
	}
	
	protected void populateQueryExprMapping(SubqueryDefinition subqueryDefn) 
	{
		Util.instance.populateQueryExprMapping(subqueryDefn);
	}
	/**
	 * Utility
	 */
	private static class Util
	{
		private static Util instance = new Util( );
		
		private static BaseExpression[] expressions;