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
/**
	 * 
	 * @param index
	 */
	public void setLeaveGroupIndex( int index )
	{
		this.leafGroupIdx = index;
	}
	/**
	 * Returns the 1-based index of the outermost group in which the current row
	 * is the last row. For example, if a query contain N groups (group with
	 * index 1 being the outermost group, and group with index N being the
	 * innermost group), and this function returns a value M, it indicates that
	 * the current row is the last row in groups with indexes (M, M+1, ..., N ).
	 * 
	 * @return The 1-based index of the outermost group in which the current row
	 *         is the last row; (N+1) if the current row is not at the end of
	 *         any group;
	 */
	public int getEndingGroupLevel( ) throws DataException
	{
		checkHasCurrentRow( );
		
		if ( this.groupCalculationUtil.getResultSetCache( ).getCurrentIndex( ) == this.groupCalculationUtil.getResultSetCache( )
				.getCount( ) - 1 )
			return 0;
		
		if ( this.groups.length == 0 )
			return 1;