misleading convergence message in minres

[campospinto]

The minres algorithm stops when ||r|| ≤ (||A|| ||x||) * tol, with the message A solution to Ax = b was found, given rtol.
However when x is very large, there is no guarantee that the "true" relative residual ||r|| / ||b|| is indeed small.
There should be an a posteriori check, and also an option to use the true relative residual.

scipy/scipy/sparse/linalg/_isolve/minres.py

Line 285 in 651a9b7

test1 = rnorm / (Anorm*ynorm) # ||r|| / (||A|| ||x||)