Issue #136: bean-format get's tripped by calculated values (blais/beancount)

[Dominik Aumayr]

New issue 136: bean-format get's tripped by calculated values
https://bitbucket.org/blais/beancount/issues/136/bean-format-gets-tripped-by-calculated

Dominik Aumayr:

`bean-format` fails with an `assert`-error when using the following simple test-file:


```
2016-08-01 open Expenses:Test
2016-08-01 open Assets:Test

2016-08-02 * "" ""
Expenses:Test 10.0/2 USD
Assets:Test
```

`bean-check` does not complain about the `10.0/2 USD`, and I think this is also explicitly supported by beancount.

But it does trip up `bean-format`.