ion successfully if
       <em class="parameter"><code>errormsg</code></em> is <code class="symbol">NULL</code>.  If
       <em class="parameter"><code>errormsg</code></em> is not <code class="symbol">NULL</code> then the
       <code class="command">COPY</code> is forced to fail, with the string pointed to by
       <em class="parameter"><code>errormsg</code></em> used as the error message.  (One should not
       assume that this exact error message will come back from the server,
       however, as the s