Bug 41927 [Dialogs] Selecting in PreferenceDialog generates too many invalid entries
20030825 If you select an entry, close the dialog and then reopen it selecting anotehr entry will result in a "this page has invalid values" although you selected nothing.
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
if (control != null) {
			size = doComputeSize();
			return size;
		}
		return new Point(0, 0);
	}
	/**
	 * Contributes additional buttons to the given composite.
	 * <p>
	 * The default implementation of this framework hook method does
	 * nothing. Subclasses should override this method to contribute buttons 
	 * to this page's button bar. For each button a subclass contributes,
	 * it must also increase the parent's grid layout number of columns
	 * by one; that is,
	 * <pre>
	 * ((GridLayout) parent.getLayout()).numColumns++);
	 * </pre>
	 * </p>
	 *
	 * @param parent the button bar
	 */
	protected void contributeButtons(Composite parent) {
	}
	/**
	 * Creates and returns the SWT control for the customized body 
	 * of this preference page under the given parent composite.
	 * <p>
	 * This framework method must be implemented by concrete subclasses. Any
	 * subclass returning a <code>Composite</code> object whose <code>Layout</code>
	 * has default margins (for example, a <code>GridLayout</code>) are expected to