Bug 129214 [Field Assist] - Decorated Field attachments not centering images horizontally
DecoratedField is supposed to center decorations horizontally on each side. The current attachments are not doing so. Also consider whether grid would have been a better choice for internal implementation.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/DecoratedField.java
FieldDecoration decoration;
		Label label;
		FormData data;
		boolean showOnFocus;
		boolean visible = true;
		/**
		 * Create a decoration data representing the specified decoration, using
		 * the specified label and form data for its representation.
		 * 
		 * @param decoration
		 *            the decoration whose data is kept.
		 * @param label
		 *            the label used to represent the decoration.
		 * @param formData
		 *            the form data used to attach the decoration to its field.
		 * @param showOnFocus
		 *            a boolean specifying whether the decoration should only be
		 *            shown when the field has focus.
		 */
		FieldDecorationData(FieldDecoration decoration, Label label,
				FormData formData, boolean showOnFocus) {
			this.decoration = decoration;