Using assign() with int (in fact, any integral type) should select the
(size_type count, const T& value) overload, but didn't, which was
incompatible with std::vector<>.
Fix this by adding the same tag-dispatching technique as used by the
real std::vector<> implementations themselves, except that we dispatch
on integer types because we can't be totally certain that
std::iterator_traits<> are specialized for whatever iterator-like object
could be used with wxVector.
9e714fdb5e