fix as described in PR #53.

fixes warnings

Seen with all versions of msvc from (at least) 9.0 up to 14.1.
Signed-off-by: Daniela Engert dani@ngrt.de

fixed pr #53, #52, #50, #49, #34, #29, #23, #25, #20, #14, #7

src/basic_iarchive.cpp

@@ -487,7 +487,7 @@ basic_iarchive_impl::load_pointer(
         m_pending.version = co.file_version;
 
         // predict next object id to be created
-        const unsigned int ui = object_id_vector.size();
+        const size_t ui = object_id_vector.size();
 
         serialization::state_saver<object_id_type> w_end(m_moveable_objects.end);