improve logic for use of mean forecast recruitment

[Rick-Methot-NOAA]

Concisely describe what has been changed/addressed in the pull request.

Improve logic controlling the use of mean forecast recruitment to all usage for years after recdev_end

• Resolves issue allow forecast mean recruitment option for late recdevs #694

What tests have been done?

Where are the relevant files?

<-- - [x] No test files are required for this pull request. -->

What tests/review still need to be done?

A comparison using petrale sole seems helpful

Is there an input change for users to Stock Synthesis?

<-- - [X] No, there was no input change. -->

Additional information (optional).

[iantaylor-NOAA]

Looks good. I have one suggested change to the error message but otherwise looks great.

I did look on what happens if you have the deprecated option Fcast_Loop_Control(3) == 3 and it seems that the setting will be automatically changed to option 4 (with a warning) before it gets to this revised code so makes sense to exclude reference to option 3 as you've done.

[Rick-Methot-NOAA]

@e-perl-NOAA
for section 6.4 of the manual:
currently is:

3 = Mean recent recruitment: calculate the mean recruitment and use it during the forecast period.

Note that bias adjustment is not applied to this mean because the values going into the mean have already been bias adjusted.

This feature affects the expected recruitment in all years after the last year of the main recruitment deviations. This means that if the last year of main recruitment deviations is before end year, then the last few recruitments, termed “late”, are also affected by this forecast option. For example, option 3 would allow you to set the last 2 years of the time series and all forecast years to have recruitment equal to the mean recruitment for the last 10 years of the main recruitment era.

revise to:

3 (deprecated) and 4 = Multiplier times mean recruitment: calculate the mean recruitment from a specified range of years and use it during the forecast and late recdev period.
This mean recruitment is applied to all years after the last year of the main recruitment deviations. Consequently, the last year from which the mean is calculated must be <= the last year for main recruitment deviations. This feature would, for example, allow a user to set the last 2 years of the time series and all forecast years to have recruitment equal to 0.75 * the mean recruitment for the last 10 years of the main recruitment era.
Note that bias adjustment is not applied to this mean because the values going into the mean have already been bias adjusted.