MacRuby issue with nested modules that use the names of objective-c classes with the C API

broken.c

mJSON = rb_define_module("JSON");
rb_define_module_under(mJSON, "NSString");
// TypeError: JSON::NSString:Class is not a module
// This seems to happen because a call to rb_const_defined_at will always resolve NSString

not-broken.c

mJSON = rb_define_module("JSON");
rb_define_module_under(mJSON, "String");

// This will work, and is a reduction of how json is coded right

not-broken.rb

module JSON
  module NSString
  end
end

p JSON::NSString.class
p JSON::NSString::NSString.class

# this works as expected, and is how json/pure is patched (changed module from String to NSString)