Fix hangups when using sockets under OS X.

Fix hangups when using sockets under OS X.

A socket event apparently doesn't count as a real event under OS X and our
wxEventLoop::DispatchTimeout() doesn't return when it happens -- so we need to
generate an artificial wake up event ourselves to make it do it and return
control to the code in wxSocket::DoWait() in order for it to process the event.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61678 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775