wxFileSystemWatcher deals with overflows in a better way.

wxFileSystemWatcher in MSW
-  now checks for overflow conditions. In the case that there are too many events and
   not all fit in the watch buffer, ReadDirectoryChangesW will discard the watch buffer.
   The watcher notifies the event handlers that an overflow occurred by generating
  a wxFileSystemWatcherEvent of type wxFSW_EVT_WARNING.
- now resumes reading directory changes when an overflow of events is encountered. This is
  pretty important, if a big directory (100+ files) was copied into a watched directory, the
  watch buffer would overflow and any new events would no longer be captured.

wxFileSystemWatcher on unix (inotify)
- now generates a warning event with type overflow

These changes are a a partial fix to http://trac.wxwidgets.org/ticket/12847
fswatcher implementation in MSW is a bit more robust

These changes allow the wxFileSystemWatcher implementation overflow less
often, it makes it possible to generate more wxFileSystemWatcherEvents
by

- increasing file changed event buffer size
- instead of asking for all events, only ask for events depending on
  the watcher/ flags.  That way we dont have to filter out events that
  the watcher did not ask for.
Merge branch 'wxFSWatcher-logging' of https://github.com/robertop/wxWidgets into wxFSWatcher-logging