reason it is implemented by delegating to File (by inheriting from
DelegateClass(File)) rather than by inheriting from it, does not
actually look like a File, and hence does not look like an IO (in
that it does not respond to kind_of? IO calls).
In ruby 1.8.5 this doesn't matter as REXML checks that the source
it has been given responds to the methods it wants (using respond_to?
which is handled properly by DelegateClass) but in 1.8.4 which we
are running on rails2 REXML uses kind_of? to see if the source is
one it can use.
