Bug 249915 [Dialogs] TitleAreaDialog does not short circuit if message is null
M20080911-1700 When profiling use of a custom WizardDialog on Linux/GTK, a lot of time was spent in WizardPage.setMessage(...). It turns out that this was because we were setting a message of null after each keypress, and the page's description (DialogPage.getDescription()) was also null. In this case the short-circuit in TitleAreaDialog.setMessage(String, int) fails to notice that the message has not changed, and does a layout every time. For our dialog this takes about 40ms each time, which is noticeable when compounded with other work.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/TitleAreaDialog.java
/*
	 * @see Dialog.createContents(Composite)
	 */
	protected Control createContents(Composite parent) {
		
		Composite contents = new Composite(parent, SWT.NONE);
		contents.setLayoutData(new GridData(GridData.FILL_BOTH));
		
		initializeDialogUnits(contents);
		FormLayout layout = new FormLayout();
		contents.setLayout(layout);
		
		workArea = new Composite(contents, SWT.NONE);
		GridLayout childLayout = new GridLayout();
		childLayout.marginHeight = 0;
		childLayout.marginWidth = 0;
		childLayout.verticalSpacing = 0;
		workArea.setLayout(childLayout);
		Control top = createTitleArea(contents);
		resetWorkAreaAttachments(top);
		workArea.setFont(JFaceResources.getDialogFont());
		
		initializeDialogUnits(workArea);
		
		dialogArea = createDialogArea(workArea);
		buttonBar = createButtonBar(workArea);
		return contents;
	}
	/**
	 * Creates and returns the contents of the upper part of this dialog (above