(detect_coding_utf_8): Check incomplete byte sequence.

(detect_coding_utf_8): Check incomplete byte sequence.
Don't update *mask when correctly detected.
(detect_coding_utf_16): Likewise.
(detect_coding_emacs_mule): Likewise.
(detect_coding_iso_2022): Likewise.
(detect_coding_sjis): Likewise.
(detect_coding_big5): Likewise.
(detect_coding_ccl): Likewise.
(decode_coding_sjis): Fix decoding of katakana-jisx0201.
(detect_eol): Delete the argument CODING, and add the argument
CATEGORY.
(detect_coding): Adjusted for the changes above.
(detect_coding_system): Likewise.