Consistently print calendar dates in the locale of the user

Calendar files that specify LANG=... to specify their character encoding did
also set the date format defined for that locale, resulting in output like:

Nov 4 Gabriel Faure dies from pneumonia in Paris, France, 1924
4 nov. N'oubliez pas les Charles !

After this commit the output is always printed in a consistent format
according to the user's current locale, e.g.:

Nov 4 Gabriel Faure dies from pneumonia in Paris, France, 1924
Nov 4 N'oubliez pas les Charles !

I'll open a review asking for opinions whether this format change should
be merged to -STABLE.

Relnotes: yes