Bug 123840 Incorrect use of static fields in NEvaluator and FilterPassController
Data Engine classes org.eclipse.birt.data.engine.script.NEvaluator and FilterPassController (used for top-n and bottom-n filter process) use static class fields to store proessing data. This is not multi-thread safe. If there are concurrent requests running in the same JVM (even if they use different instances of DataEngine), data corruption will occur since multiple requests may get/set the static fields at the same time. These classes should keep all per-request data in instance fields. Each report query need to have its own instance.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/script/ScriptEvalUtil.java
* 
	 * @param resultObject
	 * @param resultOp1
	 * @return true if resultObject is Bottom Percent,false otherwise
	 * @throws DataException
	 */
	private static boolean isBottomPercent( Object resultObject,
			Object resultOp1 ) throws DataException
	{
		return NEvaluator.getInstance( NEvaluator.BOTTOM_INSTANCE )
				.evaluate( resultObject, resultOp1, true );
	}
	/**
	 * Evaluates a IJSExpression or IConditionalExpression
	 * 	
	 * @param expr
	 * @param cx
	 * @param scope
	 * @param source
	 * @param lineNo
	 * @return 
	 * @throws DataException
	 */
	public static Object evalExpr( IBaseExpression expr, Context cx, Scriptable scope, 
				String source, int lineNo )
		throws DataException
	{
		if ( logger.isLoggable( Level.FINER ) )
			logger.entering( ScriptEvalUtil.class.getName( ),
				"evalExpr",