bug#13275: 24.2; Tramp regression: remote shells no longer work

[Dima Kogan]

I'm observing that remote tramp shells no longer work with the most
recent emacs from git. I have only tried with recent linux kernels and
amd64 machines for both the client and the server.

My HEAD is currently at 9ca828f0bb329dcc50e68f52d19f17b4e53d68dd
(gnus-related commit made on 2012/12/24), although this issue has been
around for about a month now.

To reproduce:

1. launch emacs
2. open anything with tramp. For instance C-x C-f /server:
3. M-x shell then accept the defaults for the shell and path

You'll get a shell at this point, but even though emacs thinks it is
remote, it's actually local, as can be verified with 'uname -n'. Other
remote processes other than shell-mode are affected; for instance
gud-gdb now suffers from this issue as well.

A bisection indicates that this regression was introduced on Nov 13 in
commit 46d8d668c19b4f299b49856be204a419c15c0af5 : "Use faccessat, not
access, when checking file permissions".

I haven't investigated further.

Thanks.