move comparators into mtl namespace

boost/numeric/itl/pc/comparators.hpp

 // Software License for MTL
-// 
+//
 // Copyright (c) 2007 The Trustees of Indiana University.
 //               2008 Dresden University of Technology and the Trustees of Indiana University.
 //               2010 SimuNova UG (haftungsbeschränkt), www.simunova.com.
 // All rights reserved.
 // Authors: Peter Gottschling and Andrew Lumsdaine
-// 
+//
 // This file is part of the Matrix Template Library
-// 
+//
 // See also license.mtl.txt in the distribution.
 //
 // Algorithm inspired by Nick Vannieuwenhoven, written by Cornelius Steinhardt
@@ -26,6 +26,7 @@
 
 #define POINTER long
 
+namespace mtl {
 namespace compare {
 
 /**
@@ -59,6 +60,6 @@ struct address_hasher {
 };
 
 } // end namespace compare
-
+} // end namespace mtl
 
 #endif // MTL_COMPARATORS_INCLUDE