Minor cleanup for Tramp "doas".

* doc/misc/tramp.texi (Inline methods): Add "doas" method.

* etc/NEWS: Add Tramp connection method "doas".

* lisp/net/tramp-sh.el (tramp-methods) <doas>:
Add `tramp-remote-shell-args'.

doc/misc/tramp.texi

@@ -590,6 +590,12 @@ the host returned by the function @command{(system-name)}.  See
 Similar to @option{su} method, @option{sudo} uses @command{sudo}.
 @command{sudo} must have sufficient rights to start a shell.
 
+@item @option{doas}
+@cindex method doas
+@cindex doas method
+
+This method is used on OpenBSD like the @command{sudo} command.
+
 @item @option{sg}
 @cindex method sg
 @cindex sg method

etc/NEWS

@@ -67,9 +67,13 @@ for the ChangeLog file, if none already exists.  Customize
 
 ** Tramp
 
++++
 *** New connection method "sg", which allows to edit files under
 different group ID.
 
++++
+*** New connection method "doas" for OpenBSD hosts.
+
 
 * New Modes and Packages in Emacs 25.2
 

lisp/net/tramp-sh.el

@@ -312,6 +312,7 @@ The string is used in `tramp-methods'.")
     (tramp-login-program        "doas")
     (tramp-login-args           (("-u" "%u") ("-s")))
     (tramp-remote-shell         "/bin/sh")
+    (tramp-remote-shell-args    ("-c"))
     (tramp-connection-timeout   10)))
 ;;;###tramp-autoload
 (add-to-list 'tramp-methods
@@ -415,7 +416,7 @@ The string is used in `tramp-methods'.")
 
 ;;;###tramp-autoload
 (add-to-list 'tramp-default-user-alist
-	     `(,(concat "\\`" (regexp-opt '("su" "sudo" "ksu" "doas")) "\\'")
+	     `(,(concat "\\`" (regexp-opt '("su" "sudo" "doas" "ksu")) "\\'")
 	       nil "root"))
 ;; Do not add "ssh" based methods, otherwise ~/.ssh/config would be ignored.
 ;; Do not add "plink" based methods, they ask interactively for the user.