Usage: <tt>input = [ <i>dir n</i> ] extendbox</tt>

<p>
Extend the current configuration along the <tt><i>dir</i></tt>-th 
direction (1, 2, 3 for x, y, z) by replicating it <tt><i>n</i></tt> times.

<p>
<tt>allocmultiple = <i>n</i></tt> must be set when calling <tt>readcn</tt> or <tt>makecrystal</tt>
if command <tt>extendbox</tt> will be called later.

<p>
Also see <tt>cutslice</tt>.
