RepositoryFactory should accept JNDI URL to Repository instance (not just RepositoryEngine) instance

JCR 1.0 suggested finding Repository instances in JNDI directly, using something like this:

InitialContext initCtx = new InitialContext();
Context envCtx = (Context) initCtx.lookup("java:comp/env");
Repository repository = (Repository) envCtx.lookup("jcr/local");

ModeShape's JndiRepositoryFactory can be used within web servers to deploy a ModeShape engine instance and register a particular Repository instance in JNDI.

However, JCR 2.0 changed this and instead uses the ServiceLoader mechanism and introduced a RepositoryFactory interface that allowed a different way to find a Repository instance:

Map<String, String> parameters = ...
for (RepositoryFactory factory : ServiceLoader.load(RepositoryFactory.class)) {
    repository = factory.getRepository(parameters);
    if (repository != null) break;
}

where the parameters are implementation-dependent. ModeShape expects a single "org.modeshape.jcr.URL" parameter whose value is a URL of several forms. However, the only JNDI form expects the *ModeShape engine* to be found in JNDI, and thus this is not compatible with the JndiRepositoryFactory approach described above.

Therefore, the RepositoryFactory should be changed to look for a JNDI URL that points directly to a Repository instance.