plusgroup mean size updating

[Rick-Methot-NOAA]

[Rick-Methot-NOAA]

The plusgroup size updating uses N-at-age values, but the values for the current year are not updated until after the growth is updated, so the values are out-of-sync . In a multiseason model, the updating only occurs in nseas, in which the N values are currently 0.0. This causes the time series of mean size in the plus group to be different in a single season model (where the N's exist at the time of the updating), and a multi-season model where the N's for the last season are still 0.0, so the update is just the average of the plusgroup size and the incoming size.
This is another good reason to move the plus group updating out of the growth function and into the popdyn function where it can occur at the end of the year in every year.
Also, the updating only uses the numbers-at-age from area 1. The mean size calculation is by sex-morph which is not area-specific.