(enum iso_code_class_type): Delete ISO_carriage_return.

(enum iso_code_class_type): Delete ISO_carriage_return.
(CODING_GET_INFO): Delete argument eol_type.  Callers changed.
(decode_coding_utf_8): Don't do eol converion.
(detect_coding_utf_16): Check coding->src_chars, not
coding->src_bytes.  Add heuristics for those that have no
signature.
(decode_coding_emacs_mule): Don't do eol converion.
(decode_coding_iso_2022): Likewise.
(decode_coding_sjis): Likewise.
(decode_coding_big5): Likewise.
(decode_coding_charset): Likewise.
(adjust_coding_eol_type): Return a new coding system.
(detect_coding): Don't detect eol.  Fix for utf-16 detection.
(decode_eol): In case of CRLF->LF conversion, use del_range_2 on
each change.
(decode_coding): Pay attention to undo_list.  Do eol convesion for
all types of coding-systems (if necessary).
(Vcode_conversion_work_buf_list): Delete it.
(Vcode_conversion_reused_workbuf): Renamed from
Vcode_conversion_reused_work_buf.
(Vcode_conversion_workbuf_name): New variable.
(reused_workbuf_in_use): New variable.
(make_conversion_work_buffer): Delete the arg DEPTH.
(code_conversion_restore): Argument changed to cons.
(code_conversion_save): Delete the argument BUFFER.  Callers
changed.
(detect_coding_system): New argument src_chars.  Callers changed.
Fix for utf-16 detection.
(init_coding_once): Don't use ISO_carriage_return.
(syms_of_coding): Initialized Vcode_conversion_workbuf_name and
reused_workbuf_in_use.