Update srfi-13 functions for Unicode

Update srfi-13 functions for Unicode

* libguile/srfi-13.c (MY_SUBF_VALIDATE_SUBSTRING_SPEC): new macro
  (MY_VALIDATE_SUBSTRING_SPEC_COPY): now unused, removed
  (MY_VALIDATE_SUBSTRING_SPEC_UCOPY): now unused, removed
  (REF_IN_CHARSET): new macro
  (race_error)[0]: unused, removed
  (scm_string_any, scm_string_every, scm_string_tabulate)
  (scm_substring_to_list, scm_reverse_string_to_list)
  (scm_reverse_list_to_string, scm_string_join)
  (s_scm_srfi13_substring_copy, scm_string_copy, scm_string_copy_x)
  (scm_string_pad, scm_string_pad_right, scm_string_trim)
  (scm_string_trim_right, scm_string_trim_both, scm_substring_fill_x):
  (scm_string_compare, scm_string_compare_ci): modified for
  both wide and narrow strings
  (compare_string): new function
  (scm_string_eq, scm_string_neq, scm_string_lt, scm_string_gt)
  (scm_string_le, scm_string_ge, scm_string_ci_eq, scm_string_ci_neq)
  (scm_string_ci_lt, scm-string_ci_gt, scm_string_ci_le, scm_string_ci_gt)
  (scm_substring_hash, scm_string_prefix_length, scm_string_suffix_length)
  (scm_string_prefix_length_ci, scm_string_suffix_length_ci)
  (scm_string_prefix_p, scm_string_prefix_ci_p, scm_string_suffix_p)
  (scm_string_suffix_ci_p, scm_string_index, scm_string_index_right)
  (scm_string_skip, scm_string_skip_right, scm_string_count)
  (scm_string_contains, scm_string_contains_ci, string_upcase_x)
  (scm_substring_upcase_x, scm_substring_upcase, string_downcase_x)
  (scm_string_downcase_x, scm_string_downcase, scm_string_titlecase_x)
  (scm_string_titlecase, scm_string_capitalize, scm_string_reverse)
  (scm_string_reverse_x, scm_string_map, scm_string_map_x)
  (scm_string_fold, scm_string_fold_right, scm_string_unfold)
  (scm_string_unfold_right, scm_xsubstring, scm_string_xcopy_x)
  (scm_string_replace, scm_string_tokenize, scm_string_split)
  (scm_string_filter, scm_string_delete): modified for both wide and
  narrow strings