throw stringifies the name

```
% ruby --1.8 -e 'begin throw :e; rescue Exception => e; p [e.class, e.message, (e.name rescue nil)]; end'
[NameError, "uncaught throw `e'", "e"]
```

vs MRI 1.8.7:

```
ruby -e 'begin throw :e; rescue Exception => e; p [e.class, e.message, (e.name rescue nil)]; end'
[NameError, "uncaught throw `e'", :e]
```

I'm getting this on a failing minitest test.
