The "automatic" (unmapped) grid calculation used by wave_reader
(automatic_grid in BaseCase.cpp) was in error for grids of
Chebyshev-type.  Instead of computing:

z = -Lz/2 + Lz/2*cos(pi*(0:(N-1))/(N-1))

it instead computed

z = -Lz/2 + Lz/2*cos(pi*(0:(N-1))/N)

(to use matlab-style notation).  This caused the written-out zgrid to be
in error near the bottom (max z-index) boundary.  Files using a
chebyshev-type unmapped x-coordinate would see the error as well in the
x-grid (max x-index).

This error affects only processing that uses the grid variables itself.
Within wave_reader where this was used, the automatic-generated grids
were used only for writing out; the input velocities and density were
read directly in from their corresponding files.  Likewise, SPINS
performed the "correct" differentiation internally without reference to
the grid coordinate.