po/Makevars: Add ”--from-code=UTF-8“ to XGETTEXT_OPTIONS

Otherwise xgettext will fail when it stumbles upon non-ASCII
characters in update-alternatives.pl, even if those are only
used in comments.

po/Makevars

@@ -8,7 +8,7 @@ subdir = po
 top_builddir = ..
 
 # These options get passed to xgettext.
-XGETTEXT_OPTIONS = --keyword=_ --keyword=N_ --keyword=_g
+XGETTEXT_OPTIONS = --keyword=_ --keyword=N_ --keyword=_g --from-code=UTF-8
 
 # 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