In dune-gemeotry 2.6, reference elements are passed by value instead of by
reference. This patch replaces those references by suitable decltype statements
to avoid the deprecation warning and stay compatible to the 2.5 release at the
same time.

The Fallback-implementation Dune::array has been removed from dune-common.

[bugfix] don't fail without SIONlib

See merge request !29

The backup-restore example failed if SIONlib is not found, because the
corresponding read/write methods silently do nothing. This causes the grid to
be restored from an empty stream, resulting in an error.

This patch fixes the issue by restoring the grid from the SIONlib file only if
SIONlib has been found. Otherwise, this option of restoring is silently ignored.

[gridfactory] add insertion index for LevelIntersection

See merge request !31

grid.

use infrastructure in dune-common to build Python packages

See merge request !27

In dune-common 2.6+ the infrastructure for creating Python packages is
included. This patch replaces our own infrastructure by the core
implementation

balance. This was initially changed in commit
1585c141.

[bugfix] Correct vertex indices for boundary segments on ALUGrid< 2 >

See merge request !24

Remove autotool

See merge request !21

conforming grids.

[bugfix] add missing header

See merge request !22

due to unstable and incomplete implementation practices.

GenericGeometry backport.