returns a mask not set in PRIORITIES.
(detect_eol_type_in_2_octet_form): New function.
(detect_eol): selects detect_eol_type_XXX to call according to
- cooding->category_idx.
+ coding->category_idx.
(detect_coding_system): Remove `nil' coding-system in the result.
(Fupdate_coding_systems_internal): Update all coding-categories.