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
*   remain enabled, and <code>false</code> if it should be disabled
     * @return a map containing the saved state suitable for restoring later
     *   with <code>restoreUIState</code>
     * @see #restoreUIState
     */
    private Map saveUIState(boolean keepCancelEnabled) {
        Map savedState = new HashMap(10);
        saveEnableStateAndSet(backButton, savedState, "back", false); 
        saveEnableStateAndSet(nextButton, savedState, "next", false); 
        saveEnableStateAndSet(finishButton, savedState, "finish", false); 
        saveEnableStateAndSet(cancelButton, savedState,
                "cancel", keepCancelEnabled); 
        saveEnableStateAndSet(helpButton, savedState, "help", false); 
        if (currentPage != null) {
			savedState
                    .put(
                            "page", ControlEnableState.disable(currentPage.getControl())); 
		}
        return savedState;
    }
    /**
     * Sets the given cursor for all shells currently active
     * for this window's display.
     *
     * @param c the cursor
     */
    private void setDisplayCursor(Cursor c) {
        Shell[] shells = getShell().getDisplay().getShells();
        for (int i = 0; i < shells.length; i++) {
			shells[i].setCursor(c);