Bug 180189 Support in memory data set cache.
Currently, Design-Time Data Cache is stored on disks. By performance tests using ramdisk, we found that caching in physical memory can improve the performance of RunAndRender by 30%.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/executor/DataSetCacheManager.java
{
		private File dataFile;
		private IResultClass rsClass;
		private File metaFile;
		private FileOutputStream fos;
		private BufferedOutputStream bos;
		private ResultObjectUtil roUtil;
		private int rowCount;
		/**
		 * constructor of class MergeUtil
		 * 
		 * @param file
		 * @param rsClass
		 * @throws DataException
		 */
		private MergeUtil( File dataFile, File metaFile ) throws DataException