Cut and Paste Timestamps

Methods of wx:media-buffer% which use the clipboard -- including copy, cut, paste, and do-edit -- take a timestamp parameter. This timestamp should come from the wx:mouse-event% or wx:key-event% object which triggered the clipboard action. X Windows uses the timestamp to synchronize clipboard operations among the clipboard clients.

If the timestamp is 0, it is defaulted to the ``current time''. This almost always works fine, but it is still bad manners under X Windows.