FLR

1) Secondary classes don´t always work correctly when mixing iters as 1
or n, for example having landings.sel with n iters in FLBRP means that
landings.n must also have n iters. I had major problems in fwd() when
working with FLStocks, FLBiols, FLMetiers, FLFleets, FLCatches and FLSRs
and so created some validation code, found in FLCoreVarCon.R. I think it
would be worthwhile either adding this to FLCore or creating some
protocols for use in secondary packages.

I therefore propose we look at FLCoreVarCon.R in FLBRP and add it to FLCore as a generic routine
for use in secondary packages