[[Imported from SVN: r9899]]

As of yet completely untested

[[Imported from SVN: r9898]]

[[Imported from SVN: r9897]]

The implementation uses TinyXML2.  If you don't have that installed
then a NotImplemented exception will be thrown.

The code is still pretty fragile, and needs more defensive programming.
It will probably crash on a number of well-formed files.

[[Imported from SVN: r9896]]

[[Imported from SVN: r9895]]

[[Imported from SVN: r9894]]

It is not used anymore.  On the other hand, I want to get rid of 
GeometryGrid in the CosseratVTKWriter.  Now with the new VTKFile
at hand there is a chance.

[[Imported from SVN: r9893]]

[[Imported from SVN: r9892]]

[[Imported from SVN: r9891]]

[[Imported from SVN: r9890]]

[[Imported from SVN: r9889]]

[[Imported from SVN: r9888]]

This is needed for projection-based finite elements.

The code in this patch has not been tested yet.

[[Imported from SVN: r9887]]

[[Imported from SVN: r9886]]

dune-solvers actually does provide a way to set these matrices directly.
I simply didn't find it until recently.

[[Imported from SVN: r9885]]

Currently, the only use of FD is to double check the derivatives computed
either by hand-written code or (more frequently) by automatic differentiation.
However, only multiprecision number types allow to really be sure that the
rounding/cut off errors of FD do not hide subtle errors.

Unfortunately, this patch doesn't go all the way.  It now won't run with 'double'
anymore.  Also, user code needs to be modified in small but inelegant ways
(e.g., no 'std::' prefixes for math functions).  Since the FD tests don't
have to be run every day that's okay for now.

[[Imported from SVN: r9884]]

[[Imported from SVN: r9883]]

[[Imported from SVN: r9882]]

[[Imported from SVN: r9881]]

We are using stuff from there.

[[Imported from SVN: r9880]]

[[Imported from SVN: r9879]]

[[Imported from SVN: r9878]]

[[Imported from SVN: r9877]]

That should be no problem now that we use a 50-decimal digits type
for the FD approximation.

[[Imported from SVN: r9876]]

[[Imported from SVN: r9875]]

It offers a 'double' interface, but we don't really need that.

[[Imported from SVN: r9874]]

[[Imported from SVN: r9873]]

[[Imported from SVN: r9872]]

This fixes a dubious compiler error.

[[Imported from SVN: r9871]]

[[Imported from SVN: r9870]]

This code compares scalar and vector AD, and a finite difference
approximation.

[[Imported from SVN: r9869]]

[[Imported from SVN: r9868]]

It appears that there may be very small energy increases due to
rounding errors.

[[Imported from SVN: r9867]]

Solvers from dune-solvers expect the number type to be exported
as field_type.  This patch adds the missing export to RealTuple.

[[Imported from SVN: r9866]]

This bug has now influence as long as mu_c is zero, but for
non-zero mu_c there was one term missing.

[[Imported from SVN: r9865]]

[[Imported from SVN: r9864]]

ParaView doesn't support P3 elements.  Therefore, the data is
downsampled onto a p2 space.

[[Imported from SVN: r9863]]

[[Imported from SVN: r9862]]

For some reason, when numpy is used, I can't use ctrl-c to stop
the program.  But numpy is not really used anyway, so let's get
rid of it.

[[Imported from SVN: r9861]]

[[Imported from SVN: r9860]]