Translations: Use --package-name=xz-man with po4a

This is to match reality. See the added comment.

(cherry picked from commit 75f5f2e014)

po4a/update-po

@@ -58,10 +58,17 @@ done
 # Using --porefs file and --msgmerge-opt '--add-location=file' make diffing
 # the .pot and .po files easier. If a translator prefers to have the line
 # numbers available, one may delete those options and rerun this script.
+#
+# The values from --package-name and --package-version are used to create
+# the Project-Id-Version field. It likely makes sense that its value isn't
+# identical to the value in the program message translations. In practice
+# it seems that the .po files from many (but not all) translators will use
+# "xz-man" no matter what is specified here and in xz-man.pot. Thus it's
+# best to use "xz-man" here to get the most consistent results.
 set -x
 po4a --force --verbose \
 	--porefs file --msgmerge-opt '--add-location=file' \
-	--package-name="XZ Utils" \
+	--package-name="xz-man" \
 	--package-version="$PACKAGE_VERSION" \
 	--copyright-holder="The XZ Utils authors and contributors" \
 	po4a.conf