* doc/misc/tramp.texi (File name completion): Adapt example
expanding "//".
* lisp/net/tramp.el (tramp-handle-substitute-in-file-name): "//" shall
expand the localname only, even when on top of the local part.
* test/lisp/net/tramp-tests.el (tramp-test04-substitute-in-file-name):
Adapt test.