Mac sockets events must be added to the RunLoop in the main thread, very similar...

Mac sockets events must be added to the RunLoop in the main thread, very similar to MSW.  OnInit will now statically store the main RunLoop when wxSocketBase::Initialize is called (which should be called from the main thread), allowing sockets to be created in secondary threads and still receive events

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@29672 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775