(scm_internal_parse_path): Removed.

(scm_internal_parse_path): Removed.
(scm_parse_path): Use scm_string_split to do the work.
(scm_init_load_path): Use scm_parse_path instead of
scm_internal_parse_path.
(scm_search_path): Rewritten string handling part of the code in
terms of scm_to_locale_stringbuf and so that it is thread safe.