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
/**
         * Grouping interval unit is Day.
         */
    	public static final int DAY_INTERVAL = 5;
    	
    	/**
         * Grouping interval unit is Hour.
         */
    	public static final int HOUR_INTERVAL = 6;
    	
    	/**
         * Grouping interval unit is Minute.
         */
    	public static final int MINUTE_INTERVAL = 7;
    	
    	/**
         * Grouping interval unit is Second.
         */
    	public static final int SECOND_INTERVAL = 8;
    	
    	/**
    	 * Grouping interval unit is the numerical value.
    	 */
    	public static final int NUMERIC_INTERVAL = 99;
    	
    	/**
         * Grouping interval unit is the length of the string prefix.
         */
    	public static final int STRING_PREFIX_INTERVAL = 100;