Translations: Update po/Makevars to use the template from gettext 0.22.4.

Also add SPDX license identifier now that there is a known license.

po/Makevars

@@ -1,4 +1,10 @@
+# SPDX-License-Identifier: FSFUL
+
 # Makefile variables for PO directory in any package using GNU gettext.
+#
+# Copyright (C) 2003-2019 Free Software Foundation, Inc.
+# This file is free software; the Free Software Foundation gives
+# unlimited permission to use, copy, distribute, and modify it.
 
 # Usually the message domain is the same as the package name.
 DOMAIN = $(PACKAGE)
@@ -8,7 +14,7 @@ subdir = po
 top_builddir = ..
 
 # These options get passed to xgettext.
-XGETTEXT_OPTIONS = --keyword=_ --keyword=N_
+XGETTEXT_OPTIONS = --keyword=_ --keyword=N_ --no-wrap
 
 # This is the copyright holder that gets inserted into the header of the
 # $(DOMAIN).pot file.  Set this to the copyright holder of the surrounding
@@ -20,6 +26,13 @@ XGETTEXT_OPTIONS = --keyword=_ --keyword=N_
 # their copyright.
 COPYRIGHT_HOLDER =
 
+# This tells whether or not to prepend "GNU " prefix to the package
+# name that gets inserted into the header of the $(DOMAIN).pot file.
+# Possible values are "yes", "no", or empty.  If it is empty, try to
+# detect it automatically by scanning the files in $(top_srcdir) for
+# "GNU packagename" string.
+PACKAGE_GNU = no
+
 # This is the email address or URL to which the translators shall report
 # bugs in the untranslated strings:
 # - Strings which are not entire sentences, see the maintainer guidelines
@@ -40,7 +53,35 @@ MSGID_BUGS_ADDRESS =
 # message catalogs shall be used.  It is usually empty.
 EXTRA_LOCALE_CATEGORIES =
 
-# Although you may need slightly wider terminal than 80 chars, it is
-# much nicer to edit the output of --help when this is set.
-XGETTEXT_OPTIONS += --no-wrap
-MSGMERGE += --no-wrap
+# This tells whether the $(DOMAIN).pot file contains messages with an 'msgctxt'
+# context.  Possible values are "yes" and "no".  Set this to yes if the
+# package uses functions taking also a message context, like pgettext(), or
+# if in $(XGETTEXT_OPTIONS) you define keywords with a context argument.
+USE_MSGCTXT = no
+
+# These options get passed to msgmerge.
+# Useful options are in particular:
+#   --previous            to keep previous msgids of translated messages,
+#   --quiet               to reduce the verbosity.
+MSGMERGE_OPTIONS = --no-wrap
+
+# These options get passed to msginit.
+# If you want to disable line wrapping when writing PO files, add
+# --no-wrap to MSGMERGE_OPTIONS, XGETTEXT_OPTIONS, and
+# MSGINIT_OPTIONS.
+#
+# Although one may need slightly wider terminal than 80 chars, it is
+# much nicer to edit the output of --help when --no-wrap is set.
+MSGINIT_OPTIONS = --no-wrap
+
+# This tells whether or not to regenerate a PO file when $(DOMAIN).pot
+# has changed.  Possible values are "yes" and "no".  Set this to no if
+# the POT file is checked in the repository and the version control
+# program ignores timestamps.
+PO_DEPENDS_ON_POT = yes
+
+# This tells whether or not to forcibly update $(DOMAIN).pot and
+# regenerate PO files on "make dist".  Possible values are "yes" and
+# "no".  Set this to no if the POT file and PO files are maintained
+# externally.
+DIST_DEPENDS_ON_UPDATE_PO = yes