Use global_flags instead of flags for the new-style code, so that legacy code can still use flags option. setFlags(int flags) now interprets old-style flags and sets global_flags, inner_boundary_flags and outer_boundary flags appropriately. invert_laplace() functions reverted back to just an `int flags' argument without *_boundary_flags, then use the new setFlags(flags). Legacy code should now continue to work, while the new style allows easier additions to global_flags and *_boundary_flags.