update: apply .mpdignore matches to subdirectories

Wildcard matches are directly applied to all filenames in
subdirectories without any attempt at matching relative paths.

This change is based on the following feature request:

  http://bugs.musicpd.org/view.php?id=3729

src/db/update/ExcludeList.cxx

@@ -89,6 +89,12 @@ ExcludeList::Check(Path name_fs) const
 	/* XXX include full path name in check */
 
 #ifdef HAVE_CLASS_GLOB
+	if (parent != nullptr) {
+		if (parent->Check(name_fs)) {
+			return true;
+		}
+	}
+
 	for (const auto &i : patterns)
 		if (i.Check(NarrowPath(name_fs).c_str()))
 			return true;