module.__types__ is a tuple for primitive typedefs

For certain primitive typedefs, `module.__types__` contains a tuple of types rather than a single class. For example,

```
In [2]: import thriftrw

In [3]: l = thriftrw.loader.Loader()

In [6]: m = l.loads('x', 'typedef i32 foo')

In [7]: m.__types__
Out[7]: ((int, long, numbers.Integral),)
```
