(count_utf_8_chars, count_utf_16_chars) (mtext__from_data, mtext_from_data): Add `const' to an arg.
(count_utf_8_chars, count_utf_16_chars)
(mtext__from_data, mtext_from_data): Add `const' to an arg.

xmirror/m17n-lib,xmirror/m17n-lib,xmirror/m17n-lib,xmirror/m17n-lib