LC_ALL=C for all machine readable `date` output

The script used to have LC_ALL=$date_locale for all calls to `date`.
However, this is undesirable for when $date_locale is non-English and
dates need to be machine readable, e.g. for `date --date=...` and
when generating RSS feeds.
Merge pull request #49 from Puuhinen/master

LC_ALL=C for all machine readable `date` output