Support for ISO-8859-16

Running:

```
code = IO.read('text_iso_8859_16',{ :encoding => 'ISO-8859-16', :mode => 'rb'})
code = code.encode('UTF-8')
```

On Jruby 1.7.6 gives me:

```
Encoding::ConverterNotFoundError: code converter not found for ISO-8859-16
   encode at org/jruby/RubyString.java:7597
   (root) at bugtest.rb:2
```

While on Ruby 2.0 runs flawlessly...
