Fix test failures from missing Objective-C classes on ruby-2.x

osx/objc/oc_import_openclass.rb is disabled on ruby-2.x,
then test script need to import Objective-C classes from .bundle
files by invoking OSX.ns_import(class_name).

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2532 f4f36d40-9719-0410-9868-dde021a23eda