Appends any anchor to the url if the url is not null and the url does not already contain an
anchor (url.indexOf('#') != -1). This implementation looks whether an anchor component was
set, and if so, it will append the markup id of that component. That markup id is gotten by
either calling
Component#getMarkupId() if
Component#getOutputMarkupId()returns true, or if the anchor component does not output it's id, this method will try to
retrieve the id from the markup directly. If neither is found, an
WicketRuntimeException is thrown. If no anchor component was set, but the
link component is attached to a <a element, this method will append what is in the href
attribute
if there is one, starts with a '#' and has more than one character.
You can override this method, but it means that you have to take care of whatever is done
with any set anchor component yourself. You also have to manually append the '#' at the right
place.