The old style has been deprecated for a long time, and is not
supported by dune-fufem anymore.

(In particular, the code discretizationerror.hh now requires
functions to satisfy the dune-functions function interface.)

In the wake of this, compute-disc-error.cc gets a number
of changes.  Let's hope I didn't screw up anything.

Using LocalIndexSet objects was mandatory with dune-functions-2.5
and earlier.  However, we only support 2.6 and later anyway,
so let's get rid of the backward-compatibility code.

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

It is still no function in the dune-functions sense, but at least the
basis parameter needs to be a dune-functions basis now, rather than
a deprecated dune-fufem basis.

I intend to move as much towards the dune-functions interface for functions,
and this is a first step.

This implements a global GFE function (inheriting from VirtualGridViewFunction).
However, the return value of this function is _not_ a manifold class.  Rather,
the manifold is embedded into a Euclidean space.  Hence this class is formally
simply vector valued, and can be used in error measurement routines and such.

[[Imported from SVN: r10024]]

[[Imported from SVN: r8070]]

[[Imported from SVN: r8062]]

don't let the class inherit from gridfunction because there is no derivative type implemented for functions with values in manifolds

[[Imported from SVN: r7985]]

[[Imported from SVN: r7947]]

[[Imported from SVN: r7946]]

[[Imported from SVN: r7936]]

[[Imported from SVN: r7919]]

[[Imported from SVN: r7917]]

[[Imported from SVN: r7915]]

[[Imported from SVN: r7914]]