Add `extern' for `Vcharset_ucs'.

Add `extern' for `Vcharset_ucs'.

(CHARSET_BYTE_SIZE): New inline function [moved from mule-charset.c].
(XCHARSET_BYTE_SIZE): Likewise.

(get_ccs_octet_table): New inline function.
(put_ccs_octet_table): Likewise.

(decoding_table_put_char): New inline function [moved from
mule-charset.c].
(decoding_table_remove_char): New inline function [moved from
mule-charset.c].

(decode_defined_char): Renamed from `DECODE_DEFINED_CHAR'; changed to
normal function.
(DECODE_CHAR): Use `decode_defined_char' instead of
`DECODE_DEFINED_CHAR'.