Parallel version of <tt>copyRchaintoCN</tt>, with the difference that the <tt>input</tt>
variable is no longer needed. Each CPU copy the scaled coordinates of its constrained atoms 
(specified by <tt>constrainedatoms</tt>) from <tt>SR</tt> to <tt>Rc0</tt>.

<p>
Effective only when MD++ is compiled for parallel runs, e.g. with
<tt>SYS = mpicc</tt> or <tt>SYS = mpigpp</tt>.
