(set_auto_coding_unwind): New function.

(set_auto_coding_unwind): New function.
(Finsert_file_contents): If the current buffer is empty, decide
the coding system after the file is inserted in the buffer.  If
not, insert the head and tail of a file in a temporary buffer and
call set-auto-coding-function.
(e_write): If there are carryover bytes in encoding because of
incomplete multibyte form, write them out as is.