Bug 118163 [Dialogs] - PopupDialog should define constants for zero margins
PopupDialogs traditionally use a 0 margin width and height for the grid layouts used. This should be made an API constant rather than subclasses just knowing.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/PopupDialog.java
* open is successful, or <code>CANCEL</code> if it is not. It provides
	 * framework hooks that allow subclasses to set the focus and tab order, and
	 * avoids the use of <code>shell.open()</code> in cases where the focus
	 * should not be given to the shell initially.
	 * 
	 * @return the return code
	 * 
	 * @see org.eclipse.jface.window.Window#open()
	 */
	public int open() {
		Shell shell = getShell();
		if (shell == null || shell.isDisposed()) {
			shell = null;
			
			create();
			shell = getShell();
		}
		
		
		
		adjustBounds();
		
		constrainShellSize();
		
		setTabOrder((Composite) getContents());
		
		listenToDeactivate = false;
		listenToParentDeactivate = false;
		
		if (takeFocusOnOpen) {