Naming subsystem <lookup> could use LinkRef/Reference

NameBindingAdd.installLookup() sets up the machinery so that when Context.lookup() is done it looks up the redirected name and returns it.

It should be possible to do that by binding a LinkRef, Reference or similar object into JNDI instead.

Where this could make a difference is when Context.lookupLink() is called instead.

Currently if you have
<simple name="java:/v" value="hello"/>
<lookup name="java:/a" lookup="java:/b"/>
lookupLink("java:/a") will return "hello" rather a LinkRef/Reference/whatever pointing to java:/b.

We need to decide whether a <lookup> should be considered a "link" for the purposes of lookup() or not. If it should be considered one, then we should change NameBindingAdd.installLookup() to make lookupLink() return the other value.