(Vcharset_latin_viscii): New variable.

(Vcharset_latin_viscii): New variable.
(Qlatin_viscii): New variable.
(make_charset): Don't use `decoding_table'.
(Vdefault_coded_charset_priority_list_for_font): New variable.
(Fmake_charset): Regard graphic = 2 as 256^n-set; setup byte_offset.
(Fset_charset_mapping_table): New implementation.
(syms_of_mule_charset): Add new symbol `latin-viscii'.
(vars_of_mule_charset): Add new variable
`default-coded-charset-priority-list-for-font'.
(complex_vars_of_mule_charset): Set `graphic' attribute of charset
`ucs-bmp' and `latin_viscii' to 2; change font registry of charset
`latin-viscii-lower' to "MULEVISCII-LOWER"; change font registry of
charset `latin-viscii-upper' to "MULEVISCII-UPPER"; add new charset
`latin_viscii'.