Do only one preconditioner iteration for sequential solvers
Currently sequential ISTL solver backends always do 3 preconditioner iterations and it is not possible to change that, see #138 (closed). This merge request makes two changes:
- The number of preconditioner steps can be set when creating the solver.
- The default is set to 1 preconditioner iteration.
This merge request closes issue #138 (closed)
Edited by René Heß