Remove empty code block
Use biggest_char and biggest_usv here too

Instead of hardcoding the number.
Fix printing multi-byte char to log or terminal

When printing a character to terminal or log file, we now count line
offset based on number of Unicode characters not bytes, this avoid
breaking the line inside a multi-byte character, and as a side effect
we now utilize the full line width even in the presence of such
characters.

Fixes http://sourceforge.net/p/xetex/bugs/45/
Avoid cryptic USV in error messages

“Bad USV code” is such a cryptic message, use “Bad character code” as we
do elsewhere.