Fix for de-serialization.

Using vanilla django-money, when one did the following:

./manage.py dumpdata

the values were saved properly, i.e:

{
  'amount': '12',
  'amount_currency': 'USD',
}

however, after the de-serialization:

./manage.py loaddata [fixtures]

the currencies were omitted. ( so the amount was 0 XYZ instead of 12 USD )

i have no idea (yet) how to write a test that proves that.. :/ however the following patch resolves this issue.