Instead, the FD approximation is now done in a separate class.

[[Imported from SVN: r9850]]

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]]

ADOL-C doesn't play nice with OpenMP.  Hence we have to disable
the latter for the time being.

[[Imported from SVN: r9446]]

[[Imported from SVN: r9421]]

[[Imported from SVN: r9391]]

[[Imported from SVN: r9390]]

[[Imported from SVN: r9294]]

[[Imported from SVN: r9284]]

the ones with i<=j.  The rest follows from symmetry of
the Hessian.

Needless to say, this makes the Hessian assembly quite
a bit faster.

[[Imported from SVN: r8587]]

The speed increase cause by the patch is, alas, hardly measurable.

[[Imported from SVN: r8360]]

[[Imported from SVN: r7837]]

[[Imported from SVN: r7611]]

and barycentric coordinates.  This is easy because we know the
number of element corners at compile time (I currently don't
see support for non-simplex elements at all).  This saves 
time, but not much: about 1%.

[[Imported from SVN: r7550]]

[[Imported from SVN: r7426]]

[[Imported from SVN: r7424]]

remove projection onto tangent space.  Is the variations are all tangent to the manifold you don't actually need it

[[Imported from SVN: r7422]]

[[Imported from SVN: r7391]]

[[Imported from SVN: r7390]]

Be smarter about when to compute what.  This speeds up assembly of the Hessian for harmonic maps from R^3 to S^2 by a factor of 3

[[Imported from SVN: r7389]]

[[Imported from SVN: r7388]]

Remove class specializations.  The old implementation for the UnitVector class will handle all cases

[[Imported from SVN: r7380]]

[[Imported from SVN: r7379]]

[[Imported from SVN: r7378]]

[[Imported from SVN: r7374]]

Remove a few specializations.  From now on we will assume that all target spaces can be parametrized by some sort of global embedding.  I don't see a case coming where that is not general enough

[[Imported from SVN: r7373]]

[[Imported from SVN: r7338]]

[[Imported from SVN: r7312]]

[[Imported from SVN: r7176]]

[[Imported from SVN: r7174]]

[[Imported from SVN: r7089]]

[[Imported from SVN: r6718]]

[[Imported from SVN: r6499]]

[[Imported from SVN: r6452]]

[[Imported from SVN: r6209]]

[[Imported from SVN: r5996]]

[[Imported from SVN: r5995]]

[[Imported from SVN: r5994]]

[[Imported from SVN: r5992]]

[[Imported from SVN: r5989]]

[[Imported from SVN: r5988]]