Introduce a flag to make the NF act as the OF

[Francesco Casella]

The new front-end was designed to avoid some manipulations/expansions that should be better handled by the back-end. However, until the back-end is updated accordingly, many models will be broken, see, e.g., #5083, #5084.

As an interim measure, we can add some functionality in the NF under a flag -d=NFasOF that will make sure we get the same output from the NF that we got from the OF. This flag will initially be true by default, but later on we can make it false by default, once there are time and resources to handle these cases in a better way within the back-end.

[Francesco Casella]

Alternatively, we can introduce multiple flags, one for each functionality, e.g. one for expanding binary product, one for evaluating functions of constants and structural parameters, etc., so we can change their defaults one at time as the back-end is upgraded.

I'm not sure what is the best option. I thought Adrian's proposal (just a single basket for all such functionalties) was simple and effective, but maybe having many separate flags allows to handle the transition process (which will probably be lengty) more smoothly.

[Per Östlund]

I prefer having separate flags for separate functionality. I've added -d=nfExpandOperations in 5002585 now, which seems to solve #5083. I've also flattened the whole MSL with it on, and it doesn't seem to introduce any additional issues. But we'll see what Hudson says.

I've also added the flag -d=nfEvalConstArgFuncs, but it's just a placeholder at the moment. The function evaluation needs more work before we can safely evaluate functions with constant arguments.

[Per Östlund]

Closing this as we've added a few flags to make the NF behave more like the OF, and there doesn't really seem to be any reason for keeping this ticket open.