Trend prefiltering fixes
Mostly fixes #679 (closed) and closes #255 (closed), #803 (closed), and #804 (closed). Still to be done:
- document new options once implementation is OKed
- check treatment of various options and trends in smoother used in
imcforecast.m
- Check treatment of these issues in
identification
- Adjust
convert_dyn_45_to_44
to reflect these changes