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
* A name is optional, i.e. a group could be unnamed.
         * @param groupName	The name of the group.
         */
        public void setName( String groupName )
        {
            name = groupName;
        }
        
    	/**
    	 * Returns the name of the group.
    	 * @return Name of group. Can be null if group is unnamed.
    	 */
    	public String getName()
    	{
    	    return name;
    	}
    	public void setDataType(int type)
    	{
    		this.dataType = type;
    	}
    	
    	public int getDataType()
    	{
    		return this.dataType;
    	}
    	/**
    	 * Specifies the sort direction on the group key. 
    	 * Use this method to specify a sort in the common case
    	 * where the groups are ordered by the group key only. 
    	 * To specify other types of sort criteria,