make drracket's test util use a relative path for things

inside the same collection so this file can (when other
things aren't too different) be used in a version of racket
that doesn't generally have the tests

collects/tests/drracket/private/drracket-test-util.rkt

@@ -5,7 +5,7 @@
          scheme/gui/base
          scheme/class
          scheme/contract
-         tests/utils/gui)
+         "../../utils/gui.rkt")
 
   (provide/contract 
    [use-get/put-dialog (-> (-> any) path? void?)]