COMPAT: Cast to string before raise in read_stata
In `pandas.io.stata::StataReader::_read_old_header` we
try to raise a ValueError.

I'm working on making a test, but this is buried pretty deep.
For now, `typlist` has type `List[int]`. We call

```python
','.join(typlist)
```

which errors on py3 (and python 2 I guess?). This came up in #13856, see https://travis-ci.org/pandas-dev/pandas/jobs/175705122#L1284 for the failure.

@kshedden any memory of writing this code? This is a bare `except` but it looks like the only exception that would trigger this is an `IndexError` when something in `typlist` is out of bounds on `self.TYPE_MAP`. Any hints on writing a test to exercise this code? If not I'll dig in more tonight.
I canceled the CI builds since there aren't any new tests (yet)
 Looking further, @PKEuS would have added originally in https://github.com/kshedden/pandas/commit/87d41f315f4c4ba50dde7de30e8287ab750bf13d#diff-2def41db3b4d04fb64de8313c0e6c25eR380 (the highlighted line had the necessary `str`conversion, but that was lost somewhere along the way). Sorry for the unnecessary ping Kerby.

@jreback any objections to merging this as-is (without any tests). I've verified that our current test suite doesn't touch these lines, so I'm not making anything _worse_ 😆
 lgtm. 
