The old implementation used quaternion multiplication to transport
the argument to the Lie algebra, and use the standard formula there.
However, one may as well use the formula for the unit sphere in R^4,
which is much simpler, and also faster.  I fact, this patch gives
a few percent of speedup for the overall code.

[[Imported from SVN: r9562]]

There is one copy which takes FieldVector<T,4> as its second argument.
Since EmbeddedTangentVector ( = Quaternion<T>) derives from FieldVector<T,4>,
that second implementation should work in all cases.

[[Imported from SVN: r9560]]

The methods 

Rotation<T,3> exp(const Rotation<T,3>& p, const EmbeddedTangentVector& v) 

and

otation<T,3> exp(const Rotation<T,3>& p, const Dune::FieldVector<T,4>& v)

do literally the same.  So they should be next to each other in the code.

[[Imported from SVN: r9559]]

This effectively means that we use another prolongation of the distance 
function on M into the surrounding space.  Since the prolongation does not
matter this patch should not change the algorithm behavior.  However, it
shaves off a few norm calculations and division.  I cannot really measure
any difference though.

A possible effect of this is that while all values should remain on the
manifold, they may start to 'drift away' due to numerical artifacts.
So we may have to add an occasional renormalization step eventually.

[[Imported from SVN: r9558]]

Patrizio told me on the phone today that this is the way it should be.

[[Imported from SVN: r9557]]

Because the gradient is needed anyway when computing the Hesse matrix.
Not computing it separately a second time shaves off about 8% wall time
of each iteration.

[[Imported from SVN: r9555]]

[[Imported from SVN: r9554]]

[[Imported from SVN: r9553]]

[[Imported from SVN: r9552]]

[[Imported from SVN: r9551]]

[[Imported from SVN: r9550]]

[[Imported from SVN: r9549]]

[[Imported from SVN: r9548]]

[[Imported from SVN: r9547]]

[[Imported from SVN: r9546]]

[[Imported from SVN: r9545]]

[[Imported from SVN: r9539]]

[[Imported from SVN: r9535]]

[[Imported from SVN: r9534]]

[[Imported from SVN: r9533]]

[[Imported from SVN: r9532]]

[[Imported from SVN: r9526]]

[[Imported from SVN: r9525]]

and move from GenericReferenceElement to ReferenceElement

[[Imported from SVN: r9524]]

The Weingarten map is block-diagonal for a product space.

[[Imported from SVN: r9517]]

It used to be a compile-term error, but now that we have ADOL-C support
the missing gradient is not a problem anymore.

[[Imported from SVN: r9516]]

[[Imported from SVN: r9510]]

[[Imported from SVN: r9509]]

[[Imported from SVN: r9508]]

This patch brings it back.

[[Imported from SVN: r9477]]

[[Imported from SVN: r9476]]

[[Imported from SVN: r9475]]

[[Imported from SVN: r9467]]

[[Imported from SVN: r9466]]

[[Imported from SVN: r9453]]

[[Imported from SVN: r9452]]

[[Imported from SVN: r9451]]

[[Imported from SVN: r9450]]

[[Imported from SVN: r9449]]

[[Imported from SVN: r9448]]