Fixed incorrect comment about [NSDate distantPast]. We aren't seeking to

block for an infinite amount of time but rather to not block at all.
Also added a bit of an overview since apparently the purpose of this code
was not readily apparent even with the existing comments.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@29986 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775