Allow to invoke OSX.objc_classnames with a block

    OSX.objc_classnames do |klassname|
      :
    end

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2625 f4f36d40-9719-0410-9868-dde021a23eda
Fix failure OSX::Protocol.oc_superclass on OS X 10.7 or earlier

superclass of Protocol class on OS X 10.7 or earlier is Object class.
the class is not a Cocoa class, then RubyCocoa fails to initialize
runtime from invoking OSX::Protocol.oc_superclass.

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2626 f4f36d40-9719-0410-9868-dde021a23eda