(Finsert_file_contents): Even if

(Finsert_file_contents): Even if
enable-multibyte-characters is nil, we must check `coding:' tag
and `file-coding-system-alist' to handle eol-conversion.

(Finsert_file_contents): Adjusted for the change of
struct coding_system and function decode_coding.  For normail file
reading, use code_convert_region.
(Fwrite_region): Adjusted for the change of struct coding_system.
(e_write): Adjusted for the change of encode_coding.