added localized date formats with the short form for months

this allows to format localized dates using the short format for the months.
examples:
  en: Dec 18, 2012
  de: 18. Dez. 2012

we need this shorter form. the existing localized format 'LL' uses the long format of the month which needs to much space. we prefer to have the shorter form where the months are abbreviated.

Sorry that I directly made the pull request for the developer branch. I created a feature branch for the changes, but finished the feature with git-flow before I pushed to my forked repo. I'm new to git flow. I'll try to do that the right way the next time.

Cheers,
-Andreas