Hashes & Arrays with multibyte characters raise a TypeError

It seems that a couple of the latest commits break hashes / arrays with multibyte characters. I've written a failing test case, and the error message is the following:

```
test_assoc_multibyte(TestPhpSerialize) [test.rb:102]:
Exception raised:
<#<TypeError: Unable to unserialize type 'h'>>.
```

Re-basing to 32463ff6e837b7e003fca02a98af995177471924 seems to work, and since commits since then are performance related (and not bug fixes), fixing this wasn't a high priority for the app I'm using this library in. It should be fixed, though.. Can someone help me out? :smiley: