ensure that ordering by importance is stable

The initial search results retrieved from the database already come
preordered, either by importnace or by distance. We want to keep
that order if all other things are equal.

lib/lib.php

@@ -55,7 +55,7 @@ function byImportance($a, $b)
     if ($a['importance'] != $b['importance'])
         return ($a['importance'] > $b['importance']?-1:1);
 
-    return ($a['foundorder'] < $b['foundorder']?-1:1);
+    return $a['foundorder'] <=> $b['foundorder'];
 }