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
* 
	 */
	private static class MiscUtil
	{
		/**
		 * 
		 * @param resultExpr
		 * @param resultOp1
		 * @return
		 */
		private static boolean isSameType( Object resultExpr, Object resultOp1 )
		{
			return resultExpr.getClass( ).equals( resultOp1.getClass( ) );
		}
		
		/**
		 * 
		 * @param result
		 * @return
		 */
		private static boolean isNumericOrString( Object result )
		{
			return ( result instanceof Number ) || ( result instanceof String );
		}
		/**
		 * 
		 * @param result
		 * @return
		 */
		private static boolean isDateOrString( Object result )