Metadata order non-deterministic when importing from CSV

[BrendanKOz]

I have recently changed banks, and the new one does not support OFX downloads, so I have had to resort to CSV.

The importer works fine, but when beancount-import wants to create a new transaction, the metadata is in alphabetical order (I believe i.e. date, source_desc).
However, when matching, it tries to add in the metadata in a non-consistent order (source_desc, date).
This then causes the matching to fail at a later run if the order has changed.