(get_translation_table): New function.

(get_translation_table): New function.
(translate_chars): Fix the bug of skipping annotation data.
(decode_coding): Utilze get_translation_table.
(encode_coding): Likewise.
(char_encodable_p): Translate char if necessary.
(Funencodable_char_position): Likewise.
(Ffind_coding_systems_region_internal): Setup translation table
for encode in a coding system attribute vector in advance.
(Fcheck_coding_systems_region): Likewise.
(Fdefine_coding_system_internal): Allow a symbol as translation
table.  For shift-jis type coding system, allow 4th charset.