bug#25131: thwarted from copying what one sees in Info

[Drew Adams]

> > > We could perhaps provide a command to copy that string, patches
> > > welcome.
> >
> > The string is available from the C-x = buffer.
> 
> Right.  I meant something similar to Info-copy-current-node-name.

I forgot about that command.  Maybe let `C-u' just extend it
to copy the text of such breadcrumbs (whether or not the
breadcrumbs are displayed).

Kind of like a relative file name vs an absolute file name.