Otherwise, all processes will write into the same file --> not a good idea.

[[Imported from SVN: r9776]]

Currently only for quadrilaterals.  I'll implement triangles as soon
as I need them.

Unfortunately, VTK appears to only support 8-node quadrilaterals
(without an element dof).  So the element dofs get ignored currently.

[[Imported from SVN: r9756]]

With this patch we start to differentiate according the the function
space bases of the input data.  We write P1 data as is, and downsample
P2 and P3 data onto a P1 space.

[[Imported from SVN: r9755]]

[[Imported from SVN: r9754]]

This makes visualizing wrinkles much easier.

[[Imported from SVN: r9753]]

[[Imported from SVN: r9666]]

That way, they can at least be looked at.  You won't see the intra-element
details, but frequently they are not even all this important.  Proper
subsampling of higher-order functions is more difficult and has to wait
for another day.

[[Imported from SVN: r9665]]

This will be generalized to take any Lagrange basis, to allow some form
of visualization for higher-order functions.

[[Imported from SVN: r9662]]

[[Imported from SVN: r9614]]

[[Imported from SVN: r8385]]

[[Imported from SVN: r8384]]

Much nicer: I can have the surface and the director vector fields
all in one file.

[[Imported from SVN: r8361]]

target space classes.  In particular, the coordinate type
now has to be given explicitly.

[[Imported from SVN: r8149]]

[[Imported from SVN: r7995]]

[[Imported from SVN: r7966]]