[test] use blessed way of loading an extension

Author: kares

src/spec/ruby/spec_helper.rb

@@ -21,8 +21,7 @@
 
 require 'rspec'
 
-require 'jruby'; ext_class = org.jruby.rack.ext.RackLibrary
-JRuby.runtime.loadExtension 'JRuby::Rack', ext_class.new, true
+JRuby::Util.load_ext('org.jruby.rack.ext.RackLibrary')
 
 module SharedHelpers
 
@@ -170,7 +169,7 @@ def should_not_eval_as_nil(code, runtime = @runtime) # alias
 rescue LoadError
 end
 
-# current 'library' environment (based on appraisals) e.g. :rails32
+# current 'library' environment (based on appraisals) e.g. :rails72
 CURRENT_LIB = defined?(Rails::VERSION) ?
   :"rails#{Rails::VERSION::MAJOR}#{Rails::VERSION::MINOR}" : :stub