Bug 160429 Drag the datasource and dataset and produce an error gradation in data explorer
Details: Drag the datasource and dataset and produce an error gradation in data explorer Step: 1.New 4 datasource named d1, d2, d3, d4. 2.Drag the datasource in data explorer to change the gradation. (1) Drag d1 between d2 and d3. (2) Drag d2 between d3 and d4. (3) Drag d4 between d2 and d3. (4) Drag d4 to the top. (5) Drag d3 between d1 and d2. (6) Drag d3 to the top. Actual result: (1) d1 will be move to bottom. (2) d2 will be move to bottom. (3) d4 will not be move to anywhere. (4) d4 will not be move to anywhere. (5) d3 will be move to bottom. (6) d3 will be move to bottom. Excepted result: The datasource will be move to the correct station.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/ModuleHandle.java
* message file. Each search uses a reduced form of Java locale-driven
	 * search algorithm: Language&Country, language, default.
	 * 
	 * @param resourceKey
	 *            Resource key of the user defined message.
	 * @param locale
	 *            locale of message, if the input <code>locale</code> is
	 *            <code>null</code>, the locale for the current thread will
	 *            be used instead.
	 * @return the corresponding locale-dependent messages. Return
	 *         <code>null</code> if resoueceKey is blank.
	 */
	public String getMessage( String resourceKey, ULocale locale )
	{
		return getModule( ).getMessage( resourceKey, locale );
	}
	/**
	 * Return a list of user-defined message keys. The list contained resource
	 * keys defined in the report itself and the keys defined in the referenced
	 * message files for the current thread's locale. The list returned contains
	 * no duplicate keys.
	 * 
	 * @return a list of user-defined message keys.
	 */
	public List getMessageKeys( )
	{
		return getModule( ).getMessageKeys( );
	}
	/**
	 * Returns a slot handle to work with the top-level parameters and parameter