Bug 182190 [StatusHandling] [Wizards] getControl assert on wizard page has no message
M6 If you forget to set the control on your wizard page our assert gives no feedback. We need an error message.
bundles/org.eclipse.jface/src/org/eclipse/jface/wizard/WizardDialog.java
* @param parent the parent button bar
     * @return the new Cancel button
     */
    private Button createCancelButton(Composite parent) {
        
        ((GridLayout) parent.getLayout()).numColumns++;
        Button button = new Button(parent, SWT.PUSH);
        button.setText(IDialogConstants.CANCEL_LABEL);
        setButtonLayoutData(button);
        button.setFont(parent.getFont());
        button.setData(new Integer(IDialogConstants.CANCEL_ID));
        button.addSelectionListener(cancelListener);
        return button;
    }
    /**
     * Return the cancel button if the id is a the cancel id.
     * @param id the button id
     * @return the button corresponding to the button id
     */
    protected Button getButton(int id) {
        if (id == IDialogConstants.CANCEL_ID) {
			return cancelButton;
		}
        return super.getButton(id);
    }
    /**
     * The <code>WizardDialog</code> implementation of this <code>Window</code>
     * method calls call <code>IWizard.addPages</code> to allow the current
     * wizard to add extra pages, then <code>super.createContents</code> to create
     * the controls. It then calls <code>IWizard.createPageControls</code>