Add support for arguments in emacsclient's ALTERNATE_EDITOR (Bug #25082)

* lib-src/emacsclient.c (fail): Parse ALTERNATE_EDITOR, or
corresponding command-line argument, into quote- or space-separated
tokens.  If a token starts with a quote, then it naturally is expected
to end with a quote; escaping is not supported. This is enough to cope
with the typical case of requiring the initial path to be quoted,
common on Windows where it may contain spaces.
* etc/NEWS: Document.
* doc/emacs/misc.texi: Likewise.
* doc/man/emacsclient.1: Tweak to remove the implication that only an
editor can be specified (the manual already mentions a “command”).
Fix a small error where “EDITOR” is referred to rather than
“ALTERNATE_EDITOR”.
* test/lib-src/emacsclient-tests.el: Add tests.

test/lib-src/emacsclient-tests.el

@@ -0,0 +1,50 @@
+;;; emacsclient-tests.el --- Test emacsclient
+
+;; Copyright (C) 2016 Free Software Foundation, Inc.
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+
+;;; Code:
+
+(require 'ert)
+
+(defconst emacsclient-test-emacs
+  (expand-file-name "emacsclient" (concat
+                                   (file-name-directory
+                                    (directory-file-name
+                                     (file-name-directory invocation-directory)))
+                                   "lib-src"))
+  "Path to emacsclient binary in build tree.")
+
+(ert-deftest emacsclient-test-alternate-editor-allows-arguments ()
+  (let (process-environment process-environment)
+    (setenv "ALTERNATE_EDITOR" (concat
+                                (expand-file-name invocation-name invocation-directory)
+                                " --batch"))
+    (should (= 0 (call-process emacsclient-test-emacs nil nil nil "foo")))))
+
+(ert-deftest emacsclient-test-alternate-editor-allows-quotes ()
+  (let (process-environment process-environment)
+    (setenv "ALTERNATE_EDITOR" (concat
+                                "\""
+                                (expand-file-name invocation-name invocation-directory)
+                                "\"" " --batch"))
+    (should (= 0 (call-process emacsclient-test-emacs nil nil nil "foo")))))
+
+(provide 'emacsclient-tests)
+;;; emacsclient-tests.el ends here