Fixed "automatic" grid calculation error for wave_reader

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.

src/BaseCase.cpp

@@ -175,13 +175,13 @@ void BaseCase::automatic_grid(double MinX,double MinY,double MinZ) {
 
    // Generate 1D arrays
    if (type_x() == NO_SLIP) {
-      xx = MinX+length_x()*(0.5+0.5*cos(M_PI*ii/size_x()));
+      xx = MinX+length_x()*(0.5+0.5*cos(M_PI*ii/(size_x()-1)));
    } else {
       xx = MinX + length_x()*(ii+0.5)/size_x();
    }
    yy = MinY + length_y()*(ii+0.5)/size_y();
    if (type_z() == NO_SLIP) {
-      zz = MinZ+length_z()*(0.5+0.5*cos(M_PI*ii/size_z()));
+      zz = MinZ+length_z()*(0.5+0.5*cos(M_PI*ii/(size_z()-1)));
    } else {
       zz = MinZ + length_z()*(0.5+ii)/size_z();
    }