Match types used in arrays.c to struct field types

Match types used in arrays.c to struct field types

* libguile/arrays.c
  - scm_shared_array_root: check for SCM_I_ARRAYP first.
  - scm_i_shap2ra:
    * check valid bounds in the '(lbnd ubnd) case. This makes
      (make-array 0 '(4 -3)) fail with a 'bad dimension' instead of
      with a 'wrong index' error.
    * use ssize_t for lbnd/ubnd/inc, not long.
  - scm_make_shared_array: use ssize_t for indices, not long.
  - scm_transpose_array: use size_t for ndim, not ulong.
  - scm_i_print_array: idem.