File.expand_path( 'asd', Pathname.new('uri:classloader:/') produces corrupted result

```
$ bin/jruby -rpathname -e "p File.expand_path 'asd', Pathname.new('uri:classloader:/')" 
"/home/christian/projects/active/jruby/jruby/uri:classloader:/asd"
```

expected result: `uri:classloader://asd` like from `File.expand_path('asd', 'uri:classloader:/')`
