Proxied terms using the root term

[awead]

When trying to define a term that uses the root element, such as:

[:mods, :foo, :bar]

OM will throw an error complaining that it doesn't exist. I haven't been able to figure out why, but I do have a branch with a test that explains the problem:

https://github.com/projecthydra/om/tree/root_proxy_terms