Adding support for 'degenerate' anonymous objects

We want to add support for 'degenerate' anonymous objects that don't add any new methods or fields.  This might seem trivial, but part of making it work is ensuring that calls to anonymous objects "fall through" appropriately, so that calls to methods that were on the original object still work when made on the anonymous object.  Currently xfail'd test: src/test/run-pass/anon-obj-degenerate.rs.
