Remove unnecessary grid from fluid test.
Make all construction from deck use EclipseGrid.

The deck constructor is still present, but it will construct an
EclipseGrid object instead of doing its own equivalent processing.
Add PINCH support to grid construction.
Create pointer-to-const objects.

Older gcc (4.4) does not allow conversion of shared_ptr<Foo> to
shared_ptr<const Foo>. Pointed out by @bska.
Use new constructor for EclipseGrid.
Merge pull request #633 from atgeirr/use-pinch

Unify grid construction, allow PINCH
Fix semantics of permeability assignment

Calling code relies on permeability tensors being stored in column
major order (row index cycling the most rapidly).  Honour that
requirement.  The previous assignment implied row major ordering
(column index cycling the most rapidly).  This, however, is a
pedantic rather than visible change because the surrounding code
enforces symmetric tensors whence both orderings produce the same
results when the array is viewed contiguously.
Remove obsolete comment

This comment was needed when the code was first developed, but
subsequent development has rendered it obsolete.  Remove it to avoid
confusion.
Simplify diagonal component thresholding

This commit switches the assignment

    diagonal = max(diagonal, minval)

to using a reference in the "diagonal" expression.  This guarantees
that the indexing is done once which eases maintainability.  While
here, replace the hard-coded dimension stride ('3') with the current
run-time dimension.  This is mostly for symmetry because the overall
code is only really supported in three space dimension.