Compiles and runs again.

Now to actual testing. Can we read and cotinue from and old file?

acc/mhd_solver/stencil_definition.sdh

@@ -14,6 +14,7 @@ uniform int AC_max_steps;
 uniform int AC_save_steps;
 uniform int AC_bin_steps;
 uniform int AC_bc_type;
+uniform int AC_start_step;
 
 // Real params
 uniform Scalar AC_dt;