Don't overwrite modifications to ModificationTimestampField
Review Request #9816 — Created March 21, 2018 and submitted — Latest diff uploaded
The ModificationTimestampField now tracks manual modifications to the
value so that if code manually sets a timestamp it will not be
overwritten during model save. This allows models to manage timestamps
manually in some cases without having to resort to mucking about with
save_base, etc.
Ran unit tests.