Do not replace the day value without notifying the user.
In undetermined circumstances, a fiscal year last day and month can be
replaced by the default December 31st value. Since all settings are
re-written for any setting changed, this is likely to happen in the back
of the user.
Moreover, the `_verify_fiscalyear_last_day` is not correct since it
doesn't accept February 29th, while `compute_fiscalyear_dates` handles
it.
opw-1867978
opw-1873260
Nicolas Martinelli
90cdc91638