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
* consulting the maximum decoration width.
	 * </p>
	 * <p>
	 * Clients may wish to set this value to <code>false</code> in cases where
	 * space usage is more important than alignment of fields. This value must
	 * be set before the decorations are added in order to ensure proper
	 * alignment.
	 * </p>
	 * 
	 * @param useMaximumWidth
	 *            <code>true</code> if the maximum decoration width should be
	 *            used as the size for all decorations, <code>false</code> if
	 *            only the decoration size should be used.
	 * 
	 * @see FieldDecorationRegistry#getMaximumDecorationWidth()
	 */
	public void setUseMaximumDecorationWidth(boolean useMaximumWidth) {
		useMaxDecorationWidth = useMaximumWidth;
	}
	/*
	 * Return the width appropriate for the specified decoration image.
	 */
	private int widthOf(Image image) {
		if (image == null)
			return 0;
		return useMaxDecorationWidth ? FieldDecorationRegistry.getDefault()
				.getMaximumDecorationWidth() : image.getBounds().width;
	}
}