Correct sign error in automatic generation of grids

Previously, the automatic_grid function was creating Chebyshev-type
grids with points ordered as:

{x,z} = L/2 + L/2*cos(pi*ii/(N-1))

This is incorrect.  The expected ordering is actually the reverse, or

{x,z} = L/2 - L/2*cos(...)

src/BaseCase.cpp

@@ -190,13 +190,13 @@ 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()-1)));
+        *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()-1)));
+        *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();
     }