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/ResultSetPopulator.java
* @param query
	 */
	void setQuery( BaseQuery query )
	{
		this.query = query;
	}
	/**
	 * Actually this cache is not supposed to be visible. But in report document
	 * presentation, sub query needs to find its result objects from its parent
	 * result set, so its parent cache has to be known. A better solution needs
	 * to be thought out for this issue.
	 * 
	 * TODO: enhance me
	 * 
	 * @return smartCache
	 */
	public ResultSetCache getCache( )
	{
		return this.smartCache;
	}
	/**
	 * Set the ResultSetCache of this ResultSetPopulator.
	 * 
	 * @param cache
	 */
	public void setCache( ResultSetCache cache )
	{
		smartCache = cache;
	}
	/**