[minres] Compute preconditioned residual also for initial residual

See merge request !454

Bump version to 2.9-git

See merge request !451

Make sure that the relaxation factor for smoothers never is complex.

See merge request !447

Remove signed-unsigned comparison on repartition.hh

See merge request !448

to get rid of a compiler warning.

The note

/dune-istl/dune/istl/paamg/smoother.hh:130:26: note: the ABI of
passing structure with complex float member has changed in GCC 4.4

for DefaultConstructionArgs::getArgs got me thinking. I just could not
imagine why there should be comlex value involved. Turned out we
somehow assumed that for complex the relaxation factore would be
complex, too. IMHO a relaxation factor should scale and hence be real.
This MR make ssure that the relaxation factor is never complex.

Unforntunately, then a note for std::make_pair with a
complex in repartition.hh appeared:
/usr/include/c++/8/bits/stl_pair.h:524:5: note: the ABI of passing
structure with complex float member has changed in GCC 4.4
     make_pair(_T1&& __x, _T2&& __y)

and I just resorted to constructing Pair directly. Not sure whether
this is really needed but it should not hurt and ensures more silence.

Get rid of shadowed/unused variable/typedef gcc-8 warnings

See merge request !445

Get rid of unused/shadowed variable compiler warnings.

See merge request !442

[gitignore] Ignore macOS caching files

See merge request !439

[MultiTypeBlockMatrix] Export the constructor of std::tuple

See merge request !395

[changelog] Mention SuiteSparse potentiel slowdown with openBlas

Closes #91

See merge request !437

Fixes #91

Update list of authors

See merge request !438

Cholmod: Add support for almost all matrix types

See merge request !424

This is achieved by using the flat matrix and vector forEach implementations.
The unit test is extended by a multi type example.

The routines traverse the container recursively and call a functor
at each scalar entry passing also the flat index.

Remove some warnings about unused typedefs and suggested braces

See merge request !435

IO matrixmarket for vectors of simd type

See merge request !368

[operators][cleanup] Use override keyword

See merge request !433

use the dune docker registry for the python and 'with-checking' ci test

See merge request !431

fix some headercheck issues

See merge request !430

Fix registrytest by properly including config.h

See merge request !429

Use [[maybe_unused]] instead of DUNE_UNUSED(_PARAMETER)

See merge request !427

Use std::void_t instead of Dune::void_t

See merge request !426