Use realloc() and placement new to manage vector's memory instead of

Use realloc() and placement new to manage vector's memory instead of
copying objects in T[] array. This is both more efficient and
matches std::vector<> semantics (erase() destroys the object immediately,
T doesn't have to be default-constructible).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@50996 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775