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

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.