Add reference to the copy_reg module in the See Also: section.

Doc/lib/libpickle.tex

@@ -259,3 +259,9 @@ the string past the pickled object's representation are ignored.
 This exception is raised when an unpicklable object is passed to
 \code{Pickler.dump()}.
 \end{excdesc}
+
+
+\begin{seealso}
+\seemodule[copyreg]{copy_reg}{pickle interface constructor
+registration}
+\end{seealso}

Doc/libpickle.tex

@@ -259,3 +259,9 @@ the string past the pickled object's representation are ignored.
 This exception is raised when an unpicklable object is passed to
 \code{Pickler.dump()}.
 \end{excdesc}
+
+
+\begin{seealso}
+\seemodule[copyreg]{copy_reg}{pickle interface constructor
+registration}
+\end{seealso}