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
* @param control
	 *            the control whose color is to be changed
	 * @param exclusions
	 *            a list of controls who are to be excluded from getting their
	 *            color assigned
	 */
	private void applyBackgroundColor(Color color, Control control,
			List exclusions) {
		if (!exclusions.contains(control)) {
			control.setBackground(color);
		}
		if (control instanceof Composite) {
			Control[] children = ((Composite) control).getChildren();
			for (int i = 0; i < children.length; i++)
				applyBackgroundColor(color, children[i], exclusions);
		}
	}
	/**
	 * Set the specified foreground color for the specified control and all of
	 * its children. Subclasses may override this method, but typically do not.
	 * If a subclass wishes to exclude a particular control in its contents from
	 * getting the specified foreground color, it may instead override
	 * <code>PopupDialog.getForegroundColorExclusions</code>.
	 * 
	 * @param color
	 *            the color to use as the background color
	 * @param control
	 *            the control whose color is to be changed
	 * @see PopupDialog#getBackgroundColorExclusions()
	 */