bug#20246: 25.0.50; Tramp does not show correct error message when ssh refuses to connect to host due to changed host key

[Filipp Gunbin]

When I try to connect to a host and that host's key differs from what I
have in ~/.ssh/known_hosts Tramp does not handle that correctly.

SSH suspects an attack, but in my case it is not.

I suppose Tramp could show the full error message emitted by ssh.

Filipp


*Messages*:

Tramp: Opening connection for fgunbin@<myhost> using ssh...
Tramp: Sending command `exec ssh -l fgunbin  -o ControlMaster=auto -o 
ControlPath='tramp.%C' -o ControlPersist=no -e none <myhost>'
Tramp: Waiting for prompts from remote shell...failed
Tramp: Opening connection for fgunbin@<myhost> using ssh...failed


tramp debug buffer:

16:58:00.853274 tramp-process-one-action (5) # Looking for regexp "\(\)\'" from 
remote shell
16:58:00.853332 tramp-process-one-action (5) # Call `tramp-action-process-alive'
16:58:00.853511 tramp-process-actions (6) # 
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
SHA256:<fingerprint>.
Please contact your system administrator.
Add correct host key in /Users/fgunbin/.ssh/known_hosts to get rid of this 
message.
Offending ECDSA key in /Users/fgunbin/.ssh/known_hosts:67
ECDSA host key for <myhost> has changed and you have requested strict checking.
Host key verification failed.
16:58:00.853619 tramp-process-sentinel (5) # Sentinel called: `#<process 
*tramp/ssh fgunbin@<myhost>*>' `exited abnormally with code 255
'
16:58:00.855144 tramp-process-actions (1) # File error: Tramp failed to 
connect.  If this happens repeatedly, try
    `M-x tramp-cleanup-this-connection'
16:58:00.855824 tramp-maybe-open-connection (3) # Opening connection for 
fgunbin@<myhost> using ssh...failed
16:58:00.858610 tramp-get-remote-perl (5) # Finding a suitable `perl' command
16:58:00.858762 tramp-file-name-handler (1) # Suppress received in operation 
(file-name-all-completions var /ssh:fgunbin@<myhost>:/)
16:58:00.861488 tramp-get-remote-perl (5) # Finding a suitable `perl' command
16:58:00.861661 tramp-file-name-handler (1) # Suppress received in operation 
(file-name-all-completions  /ssh:fgunbin@<myhost>:/)


Usual bug-report stuff:

In GNU Emacs 25.0.50.1 (x86_64-apple-darwin14.1.0)
 of 2015-03-12 on fgunbin.local
Repository revision: 2401274b239e837ec274b373ba0f2848faaea7b2
Configured using:
 `configure --without-all --with-xml2 --without-x --with-wide-int'

Configured features:
LIBXML2