Implement preconditionners as in UMFITER and ITERSTACK:
– For UMFITER, on first iteration, do a full LU decomposition, and use it as a preconditionner
  in further iterations (similar to UMFITER in TROLL).
– For ITERSTACK, build a preconditionner based on small LU decomposition
  repeated several times across the stack

By the way, uniformize the preconditioners for solve_algo={7,8} across the
different implementations.

TODO:
– make sure we have a good default for options_.simul.iter_tol. The gmres and bicgstab
  functions default to 1e-6. The run_block_bytecode_tests needs 1e-7. And
  GIMF/GMMET need 1e-12 in the block-decomposed version (partly because tolf=1e-8
  there)
– add tests for the three preconditioners (and ideally their suboptions)
– documentation

 identification: shut off slice_initialize_with_mode option with slice to prevent crash

Closes #1957

See merge request !2356

Closes #1957

– gracefully error out when a PAC model is not used in a pac_expectation
  operator
– fix handling of model local variable in DataTree copy constructor

[skip ci]

In particular, this now removes float.h which was conflicting with the one from
a recent MinGW snapshot.

By the way, rename “stop” variable to “converged” for clarity.

Ref. !2353

[CI skip]

 OccBin: disable incompatible options

See merge request !2352

Ref. !2351

Perfect foresight: improve sanity checks for linear_approximation and endogenous_terminal_period options

 Fix crash of perfect foresight w/ expectation errors + marginal linearization + several learnt_in blocks

[skip ci]

Ref. !2350

Prevents cryptic crashes

Leads to a simpler code.

I am not sure I want to repair this...

Hybrid stochastic extended path with the constant correction in the
reduced form of the model approximated at order k>1 (perturbation
around the deterministic steady state).

In each iteration using the solution from previous step. Previously
the initial guess for the auxiliary stochastic perfect forsight model
was the steady state in all periods and (future) worlds.

The initial condition of the state variables was not updated in each iteration.

For some reason, the path expected by the -B option of gfortran should now
be in Windows format (i.e. begin with the drive letter).

[skip ci]

 discretionary_policy: fix noprint option

See merge request !2349

Output argument and return statement were missing

 fix loop in kalman_update_engine.m if regime_start hits 0

Closes #1956

See merge request !2348