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
assert propHandle != null;
		return propHandle.iterator( );
	}
	/**
	 * Includes one library with the given library file name. The new library
	 * will be appended to the library list.
	 * 
	 * @param libraryFileName
	 *            library file name
	 * @param namespace
	 *            library namespace
	 * @throws DesignFileException
	 *             if the library file is not found, or has fatal error.
	 * @throws SemanticException
	 *             if error is encountered when handling
	 *             <code>IncludeLibrary</code> structure list.
	 */
	public void includeLibrary( String libraryFileName, String namespace )
			throws DesignFileException, SemanticException
	{
		LibraryCommand command = new LibraryCommand( module );
		command.addLibrary( libraryFileName, namespace );
	}
	/**
	 * Drops the given library from the included libraries of this design file.
	 * 
	 * @param library
	 *            the library to drop
	 * @throws SemanticException
	 *             if error is encountered when handling