Bug 119340 [PopupDialog] - need constant for horizontal spacing
PopupDialog provides a constant for vertical spacing used in the contents, but not for horizontal spacing.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/PopupDialog.java
* @return the Control that should receive focus when the popup opens.
	 */
	protected Control getFocusControl() {
		return dialogArea;
	}
	/**
	 * Sets the tab order for the popup. Clients should override to introduce
	 * specific tab ordering.
	 * 
	 * @param composite
	 *            the composite in which all content, including the title area
	 *            and info area, was created. This composite's parent is the
	 *            shell.
	 */
	protected void setTabOrder(Composite composite) {
		
	}
	/**
	 * Returns a boolean indicating whether the popup should have a title area
	 * at the top of the dialog. Subclasses may override. Default behavior is to
	 * have a title area if there is to be a menu or title text.
	 * 
	 * @return <code>true</code> if a title area should be created,
	 *         <code>false</code> if it should not.
	 */
	protected boolean hasTitleArea() {
		return titleText != null || showDialogMenu;
	}
	/**
	 * Returns a boolean indicating whether the popup should have an info area