SWIG: use a typedef to check the size of structs when viewing arrays

- swiglal_field_count_... #defines do not get passed to dependent SWIG
  modules, so typemaps will only work in library where array type is
  defined, e.g. REAL8Vector viewing will only work in LAL
- Instead create a dummy typedef sizechk_t containing only fields that
  should be in array type, then check if it's the same size as NAME.
  Not completely foolproof because of alignment issues, but anyway...
SWIG: fix bugs in getting pointers to Octave array data for viewing