(SCM_IS_UVEC): New, use it instead of

(SCM_IS_UVEC): New, use it instead of
SCM_SMOB_PREDICATE in this file.
(is_uvec): Also recognize one-dimensional uniform numeric arrays
of the right type.
(scm_is_uniform_vector): Likewise.
(uvec_fast_ref): Made BASE param const.
(uvec_writable_elements, uvec_elements): New.
(uvec_to_list, uvec_ref, uvec_set_x, uvec_length,
scm_c_uniform_vector_length, scm_c_uniform_vector_ref,
scm_c_uniform_set_x): Use them to also deal with one-dimensional
arrays.
(scm_uniform_vector_ref, scm_uniform_vector_set_x): Deprecate old
argument convention.
(scm_uniform_vector_to_list): Let uvec_to_list do all the
checking.
(scm_uniform_vector_length): Use uvec_length.