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

gcc warns about some of those nowadays.

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.

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

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

I want the interpolation rule to appear in the log files.
It is to easy to use the wrong one by accident.

Otherwise certain matrix-copying methods will not work anymore.

Makes the code a bit shorter and easier to read.

Only cmake is supported from now on.

Make them a parameter instead.  This allows to switch more easily between
geodesic finite elements and projected finite elements.

Make them a parameter instead.  This allows to switch more easily between
geodesic finite elements and projected finite elements.

Otherwise, the ParaView 'glyph' filter won't recognize the direction fields.