Danish localflavor

I corrected the things that were pointed out in
https://github.com/django/django-localflavor/pull/48
No additional tests were added.

I'm not quite sure why valberg chose to let the Danish/Greenland zip codes be in the string along with the name of the city.

I had considered to add a Field for Danish CPR number, but because the year is two-digit, and the information about the century is ambiguous, I'll let that problem remain open. Danish CPR numbers are in the form DDMMYY-XXXX where the 7th digit can be used for determining the century in which the person was born.