[XeTeX] newcommand with optional arguments

[Sven Siegmund]

Well, actually I had do change it a bit: The whitespace shoud have
been put to the else stuff:

\newcommand{\nuu}[2][]{%
       \textit{#2}%
       \ifx#1\empty
       \else
              \ `#1'
       \fi
}

S.