[XeTeX] hyperref bookmark problem

[Dohyun Kim]

Hi,

Compiling the following code with xelatex renders incorrect character
in bookmark pane:
the ligature character of `--' is broken.

On the other hand, if I load hyperref package with [unicode] option,
`--' character becomes well displayed in bookmark; but now Korean
characters are broken.

Please inspect the problem.

----------
\documentclass{article}
\usepackage{fontspec}
\setmainfont[Mapping=tex-text]{UnBatang} % UnBatang is a Korean
truetype font shipped with many linux distributions.
\usepackage{hyperref}
\begin{document}
\section{1997년--2001년}
\end{document}
----------