proper usage of size_t

[[Imported from SVN: r458]]

istl/bvector.hh

@@ -403,7 +403,7 @@ namespace Dune {
     }
 
     //! dimension of the vector space
-    int N () const
+    size_type N () const
     {
       return block_vector_unmanaged<B,A>::N();
     }