[FORTRAN PATCH] PR 30404: Rewrite nested FORALL mask expansion

[FX Coudert]

> For what it's worth, I can add my OK to Steve's.  In fact, I think  
> that
> it is a bug of such seriousness that if trunk survives it for a couple
> of weeks, 4.2 should be patched too.

While not competent to review the patch itself, I've thoroughly read  
the description and related explanations, and I also think it is well  
suited for 4.2.

FX