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/executor/cache/SmartCacheHelper.java
/**
	 * @param cacheRequest
	 * @param odiAdapter
	 * @param rsMeta
	 * @throws DataException
	 */
	ResultSetCache getResultSetCache( CacheRequest cacheRequest,
			OdiAdapter odiAdapter, IResultClass rsMeta ) throws DataException
	{
		initInstance( cacheRequest, odiAdapter, rsMeta );
		return this.resultSetCache;
	}
	/**
	 * @param cacheRequest
	 * @param rowResultSet
	 * @param rsMeta
	 * @throws DataException
	 */
	ResultSetCache getResultSetCache( CacheRequest cacheRequest,
			IRowResultSet rowResultSet, IResultClass rsMeta )
			throws DataException
	{
		this.eventHandler = cacheRequest.getEventHandler( );
		populateData( rowResultSet, rsMeta, cacheRequest.getSortSpec( ) );
		return this.resultSetCache;
	}
	/**
	 * Init resultSetCache
	 * 
	 * @param odiAdpater