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/odi/IQuery.java
* @param sortSpecs		An ordered list of IQuery.SortSpec objects.
     * @throws DataException	if given sortSpecs is invalid.
     */
    public void setOrdering( List sortSpecs ) throws DataException;
 	
    /**
	 * Specify the grouping of query results for aggregates.
     * @param groupSpecs	An ordered list of IQuery.GroupSpec objects.
     * @throws DataException	if given groupSpecs is invalid.
     */
    public void setGrouping( List groupSpecs ) throws DataException;
    
    /**
     * Specifies the maximum number of detail rows that can be retrieved by this query.
     * @param maxRows	Maximum number of rows. 
     * 					A value of 0 means no limit on how many rows this query can retrieve.
     */
    public void setMaxRows( int maxRows );
    
    /**
	 * Set up the max number of rows that the data set represent by this
	 * IBaseDataSetDesign instance can fetch from data source. If the input 
	 * number is non-positive then unlimited number of rows will be fetched.
	 * 
	 * @param limit
	 */
    public void setRowFetchLimit( int limit );
    
    /**
     * Define a custom event object, which is called after the query retrieves a result object