(looking_at_1): Use current_buffer->case_canon_table,

(looking_at_1): Use current_buffer->case_canon_table,
not DOWNCASE_TABLE.
(string_match_1): Likewise.
(fast_c_string_match_ignore_case): Use Vascii_canon_table, not
Vascii_downcase_table.
(fast_string_match_ignore_case): Likewise.
(search_buffer): Fix checking of boyer-moore usability.
(boyer_moore): Calculate translate_prev_byte1/2/3 in advance.  No
need of tranlating characters in PAT.  Fix calculation of
simple_translate.