Fix Bug#23614.

* lisp/net/tramp-sh.el (tramp-maybe-open-connection):
Let-bind `process-coding-system-alist' in order to suppress
the value for "cmdproxy".

* lisp/net/tramp.el (tramp-encoding-shell):
`w32-shell-name' is a function.
(tramp-encoding-command-switch)
(tramp-encoding-command-interactive): Use `w32-shell-dos-semantics'.

* test/lisp/net/tramp-tests.el (tramp-test24-file-name-completion):
Suppress some tests on MS Windows.  (Bug#23614)

lisp/net/tramp-sh.el

@@ -4790,6 +4790,9 @@ connection if a previous connection has died for some reason."
 		     (options (tramp-ssh-controlmaster-options vec))
 		     (process-connection-type tramp-process-connection-type)
 		     (process-adaptive-read-buffering nil)
+		     ;; There are unfortune settings for "cmdproxy" on
+		     ;; W32 systems.
+		     (process-coding-system-alist nil)
 		     (coding-system-for-read nil)
 		     ;; This must be done in order to avoid our file
 		     ;; name handler.

lisp/net/tramp.el

@@ -120,9 +120,7 @@ This setting has precedence over `auto-save-file-name-transforms'."
 		 (directory :tag "Auto save directory name")))
 
 (defcustom tramp-encoding-shell
-  (if (boundp 'w32-shell-name)
-      (symbol-value 'w32-shell-name)
-    "/bin/sh")
+  (or (tramp-compat-funcall 'w32-shell-name) "/bin/sh")
   "Use this program for encoding and decoding commands on the local host.
 This shell is used to execute the encoding and decoding command on the
 local host, so if you want to use `~' in those commands, you should
@@ -145,14 +143,15 @@ use for the remote host."
   :group 'tramp
   :type '(file :must-match t))
 
-(defcustom tramp-encoding-command-switch (if (boundp 'w32-shell-name) "/c" "-c")
+(defcustom tramp-encoding-command-switch
+  (if (tramp-compat-funcall 'w32-shell-dos-semantics) "/c" "-c")
   "Use this switch together with `tramp-encoding-shell' for local commands.
 See the variable `tramp-encoding-shell' for more information."
   :group 'tramp
   :type 'string)
 
 (defcustom tramp-encoding-command-interactive
-  (unless (boundp 'w32-shell-name) "-i")
+  (unless (tramp-compat-funcall 'w32-shell-dos-semantics) "-i")
   "Use this switch together with `tramp-encoding-shell' for interactive shells.
 See the variable `tramp-encoding-shell' for more information."
   :version "24.1"

test/lisp/net/tramp-tests.el

@@ -1380,8 +1380,10 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
 
       (unwind-protect
 	  (progn
-	    ;; Method and host name in completion mode.
-	    (when (tramp-completion-mode-p)
+	    ;; Method and host name in completion mode.  This kind of
+	    ;; completion does not work on MS Windows.
+	    (when (and (tramp-completion-mode-p)
+		       (not (memq system-type '(cygwin windows-nt))))
 	      (unless (zerop (length method))
 		(should
 		 (member