If <tt>allocmultiple = <i>n</i></tt> is set before <tt>
readcn</tt> or <tt>makecrystal</tt>, then the memory for <tt>NP</tt> &lowast; 
<i>n</i> atoms is allocated, where <tt>NP</tt> is the actual number of atoms.

<p>
Useful for <tt>extendbox</tt>.
