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

The formula for the FD gradient never took the distance between
the two Lagrange points into account, even though the gradient
of an interpolation function clearly depends on it.

(cherry picked from commit 7f326ded)

Previously, the actual projection happened by calling the constructor
of one of the classes that implements points on a manifold.  This patch
introduces an new method projectOnto, which makes the projection more
explicit.

So far: 2d only