Replace unsigned with appropriate type

Replace unsigned with object_numberingt::number_type, which actually
resolves to size_t rather than unsigned. This matches cbmc#1541.

Author: Owen Jones

src/pointer-analysis/local_value_set.cpp

@@ -336,7 +336,7 @@ void local_value_sett::assign(
     // initialiser from an external set that has been read from somewhere
     // and then written.
 
-    std::vector<std::pair<unsigned, exprt>> replacements;
+    std::vector<std::pair<object_numberingt::number_type, exprt>> replacements;
     for(const auto &obj : values_rhs.read())
     {
       const exprt &objexpr=object_numbering[obj.first];