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/group/GroupCalculationUtil.java
return this.groupInformationUtil;
	}
	/**
	 * @param inputStream
	 * @throws DataException 
	 */
	public void doSave( OutputStream outputStream ) throws DataException
	{
		try
		{
			this.groupInformationUtil.saveGroupsToStream( outputStream );
		}
		catch ( IOException e )
		{
			throw new DataException( ResourceConstants.RD_SAVE_ERROR,
					e,
					"Group Information" );
		}
	}
	/**
	 * Everytime in CachedResultSet the result set cache changed, it must be
	 * reset to GroupCalculationUtil. Set the value of smartCache.
	 * 
	 * @param rsc
	 */
	public void setResultSetCache( ResultSetCache rsc )
	{
		this.smartCache = rsc;
	}
	/**