It was implemented for Audacious only to open companion NWA files, but
current version has no need for it. In case there is some obscure thing
that needs it, Audacious's vfs.cc should translate or return realnames
transparently, without having to modify other streamfiles.
Handle new VFSFile throwing an error correctly, which requires checking the m_impl status of VFSFile. Conveniently, there's a bool operator on the class exactly for that purpose.
