ADOL-C implements most standard math functions for its
'adouble' type, and they are not in the namespace 'std'.
dune-fufem contains a file adolcnamespaceinjections.hh
which imports some of these methods into the 'std'
namespace, but that is not the proper way to do it.
Rather, they should be found by argument-dependent
lookup (ADL), that is

  using std::sin;
  auto v = sin(x);

The computation of the A-orthogonal matrices was wrong,
and for some reason nobody ever really noticed this.
One reason could be that in GFE applications A is frequently
very close to the identity, and then you wouldn't notice
the bug that much.

Anyway, localgeodesicfefunctiontest.cc passes now.

That's obviously more efficient when solving one linear equation
with multiple right hand sides.

[[Imported from SVN: r9836]]

[[Imported from SVN: r9601]]

[[Imported from SVN: r9582]]

Nice, because it works for rank-deficient matrices.

And still fast enough for the systems I am considering here.

[[Imported from SVN: r9580]]