Bug 211839 String grouping unit type needs to support interval range.
Build ID: I20071101-2000 As Chart has supported, the String grouping unit type can be set interval range, the interval range means that the string group will base on row count distinction. For instance, let's say we have a,b,c,d,e,f,g , and set interval range to 2, the grouping result should be a,c,e,g. Now it is a requirement that DtE support the grouping type.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/executor/transform/ResultSetPopulator.java
* Populate the result set. In this method we would firstly prepare the data
	 * needed to be used in population process, then call doPopulate method to
	 * carry out the actual population job.
	 * 
	 * @param odaResultSet
	 * @param stopSign
	 * @throws DataException
	 */
	public void populateResultSet( OdiResultSetWrapper odaResultSet, StopSign stopSign ) throws DataException
	{
		PassManager.populateResultSet( this, odaResultSet, stopSign );
	}
	/**
	 * Use the given OrderingInfo, re-set the smartCache
	 * 
	 * @param odInfo
	 * @param stopSign
	 * @throws DataException
	 */
	public void reSetSmartCacheUsingOrderingInfo( OrderingInfo odInfo, StopSign stopSign )
			throws DataException
	{
		reSetCache( odInfo, stopSign );
		this.groupProcessorManager.getGroupCalculationUtil( )
				.getGroupInformationUtil( )
				.doGrouping( stopSign );
		this.getCache( ).next( );
	}
	/**
	 * @param odInfo