FrontEvolution mixup on time units.

[citibeth]

@ckhroulev When FrontEvolution creates an output file, units are in days since...; but data are written in terms of seconds since...

See line 136 of: https://github.com/pism/uafgi/blob/eaf/develop/uafgi/pism/calving.py

See attached output file.
calving.txt