When running Norne with the interleaved solver sometimes exceptions
(diagonal matrix block is not invertible) occur for some rows in the
ILU decomposition. In a parallel run this means that some, but not all
processes will see the exceptions. This leads to a classic deadlock.
With this commit we catch the exception during the setup of the preconditioner,
determine with the other processes whether there were any exceptions, and
in this case all the processes will throw an exception.
Currently this limited to Dune::MatrixBlockError, but we could extend this.
It holds a reference to the sequential code. Previously this reference
point to a temporary object that was deleted upon exit of
constructPrecond.
With this commit use a unique_ptr to store the parallel
preconditioner. It also gets a custom deleter that will delete the
nested sequential iterator during destruction.
The current implementation avoids the using of formEllipticSystem() and
vercatCollapseJacs(), which take a significant amount of computing time
during the non-linear solutions.
