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/GroupInformationUtil.java
void saveGroupsToStream( OutputStream outputStream ) throws IOException
	{
		int size = groups.length;
		IOUtil.writeInt( outputStream, size );
		for ( int i = 0; i < size; i++ )
		{
			List list = groups[i];
			int asize = list.size( );
			IOUtil.writeInt( outputStream, asize );
			for ( int j = 0; j < asize; j++ )
			{
				GroupInfo groupInfo = (GroupInfo) list.get( j );
				IOUtil.writeInt( outputStream, groupInfo.parent );
				IOUtil.writeInt( outputStream, groupInfo.firstChild );
			}
		}
	}
	/**
	 * The structue of a groupBoundaryInfoArray is exactly same as that of
	 * GroupCalculationUtil.groups,except that all GroupInfo instances are
	 * replaced by GroupBoundaryInfo instances.
	 * 
	 * @return
	 * @throws DataException
	 */
	List[] getGroupBoundaryInfos( ) throws DataException
	{
		List[] groupBoundaryInfos = new List[groups.length];
		for ( int i = 1; i <= groups.length; i++ )
		{