Made EndpointAddress virtual

Trying again to make EndpointAddress virtual.  Sorry, there's still some differences in line endings or something.  I tried for 20 min to get rid of them and show only the one line change, but I just don't know Git well enough.  I can just log a bug instead if that's easier, or we can build our own custom version for our purposes.
This is the only line that should change.  Ignore any other file changes.