Issue #339: Reduction should take whole transaction into account (blais/beancount)

[Martin Michlmayr]

New issue 339: Reduction should take whole transaction into account
https://bitbucket.org/blais/beancount/issues/339/reduction-should-take-whole-transaction

Martin Michlmayr:

I get:

```
Ambiguous matches for "-11.48 EUR {1.0832 USD}": 11.48 EUR {1.0832 USD, 2016-02-02}, 11.48 EUR {1.0832 USD, 2016-01-31}
```

but if you look at the example, both of these 11.48 EUR are reduced in the same transactions. Since we're reducing all of them in one reduction, there shouldn't be any ambiguity.