Add the marine/tongues "example".

This is more of a test setup (the kind of test that requires
eyeballing, though).
Try to avoid overflow in IceGrid::check_parameters().

The 3D grid has to take less than 2^32-4 bytes of storage to be able to
fit in a single variable in a NetCDF-3 file. On some machines (this one
included) 2^32-4 is too close to the max. number that fits in an 'int',
so we use 'long int' instead.