unescape tag names

Since tag names are now retrieved from the file names, we must revert
the escaping process that santizes the file names. Solve by adding a
`pagetitle()` call at the end of the tagname()
(cherry picked from commit 0ee0612b1ab11d76eb3790c8db7a2ba992c54f6b)

IkiWiki/Plugin/tag.pm

@@ -63,7 +63,7 @@ sub tagname ($) {
 	} else {
 		$tag =~ s!^\.?/!!;
 	}
-	return $tag;
+	return pagetitle($tag, 1);
 }
 
 sub htmllink_tag ($$$;@) {