Make wxListCtrl sort function take wxIntPtr, not long, arguments.

Make wxListCtrl sort function take wxIntPtr, not long, arguments.

As the arguments to the sort function contain the client data associated with
the items, they may be pointers and hence of greater size than long in Win64
builds. Use wxIntPtr instead of long everywhere to fix this.

Notice that this doesn't break compatibility for 32 bit code where long can
still be used as it is the same as wxIntPtr there after the previous commit.

Closes #4309.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67733 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775