Make copy constructor public.

based on: http://forums.gentoo.org/viewtopic-p-4120030.html#4120030

--- STLport-5.1.4/stlport/stl/_valarray.h~	2006-04-05 22:34:29.000000000 +0200
+++ STLport-5.1.4/stlport/stl/_valarray.h	2007-11-05 10:11:13.528187997 +0100
@@ -1193,6 +1193,7 @@
   }
 
   ~slice_array() {}
+  slice_array(const slice_array&);
 
 private:
   slice_array(const slice& __slice, valarray<_Tp>& __array)
@@ -1204,7 +1205,6 @@
 
 private:                        // Disable assignment and default constructor
   slice_array();
-  slice_array(const slice_array&);
   slice_array& operator=(const slice_array&);
 };