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/GroupBy.java
}
	/**
	 * Determines if the current group key is in the same group as the key value
	 * provided in the last call. This method can be overrided in special case,
	 * for example, group on row position.
	 * 
	 * @param currentGroupKey
	 * @param previousGroupKey
	 * @param groupStartValue
	 * @param currRowPos
	 * @return boolean value
	 * @throws DataException
	 */
	public boolean isInSameGroup( Object currentGroupKey, Object previousGroupKey,
			Object groupStartValue, int currRowPos ) throws DataException
	{
		return isInSameGroup( currentGroupKey, previousGroupKey );
	}
	/**
	 * Determines if the current group key is in the same group as the key value
	 * provided in the last call
	 * 
	 * @param currentGroupKey
	 * @param previousGroupKey
	 * @return boolean
	 * @throws DataException
	 */
	public boolean isInSameGroup( Object currentGroupKey, Object previousGroupKey )
			throws DataException
	{