Calculate the seconds since the epoch manually
Calculate the seconds since the epoch manually

This change is needed since the time library of Python 2.7 does not
support years < 1900, but it's possible to calculate the seconds for
easlier dates and then construct datetime objects based on these values.

opendata-swiss/ckanext-switzerland,opendata-swiss/ckanext-switzerland,ogdch/ckanext-switzerland,ogdch/ckanext-switzerland,opendata-swiss/ckanext-switzerland,ogdch/ckanext-switzerland