Composite ClipNotify fix and expose event elimination

[ville.syrjala at nokia.com]

Rather than continue my attempts to hack around the issue of incorrect
ClipNotifys during window redirection changes, I decided to tackle the
issue in more proper manner.

This series will remove the internal MapWindow+UnmapWindow cycle and
replace it with a single ValidateTree+HandleExposures pass through
the affected windows.

As a nice bonus, this also eliminates the unnecessary expose events
that are generated in the process. Those expose events have been a
problem for us for quite some time. For the N900 Daniel did a hack that
simply suppressed expose events around the MapWindow/UnmapWindow calls.