Allow iterating over wxCmdLineParser arguments in order.

This allows the meaning of the options to depend on their order relatively to
the other options which wasn't possible before.

See http://review.bakefile.org/r/557/

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75723 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775