In many cases it is not needed, but I am too lazy to write
a proper test for it right now.

Good to measure whether there is locking, and whether the code works
at all.

gcc warns about some of those nowadays.

This got introduced in dune-grid 2.6.

In particular, MonotoneMultiGridStep use shared_ptr much more
frequently now.  Also, various of its data members are now
protected, and getters/setters have to be used.

It used to be in dune-functions originally, but got moved to
dune-common eventually.  This patch updates the code to reflect
that move.

Otherwise some dune-common stuff will not work properly,
for example copying of FieldMatrices that use adouble
as their number type.

I think they used to have one, back in the day of the EntityIterator
class.

Transformed the surrounding loop to range-based-for syntax
while I am there.

The method indexSet has been removed from dune-functions
a long time ago.

The one in the Arithmetic namespace does not exist anymore.

And bump required cmake version to 2.8.12.

And some other Dune 2.4 stuff.

Bugfix/fix rotationtest

Closes #1

See merge request !5

This fixes #1

It has been removed from dune-functions in the last release
(at least).

Fix method 'difference'

See merge request !1