Wiki: show 'preview' not 'current' version when 'edit' pane toggled during editing

[ThomasAkam]

When editing the wiki if you use the 'toggle view' button to hide the 'edit' pane, the 'view' pane switches back to showing the 'current' version of the page rather than the 'preview' version. As it is useful to toggle on and off the 'edit' pane during editing in order to see what the page will look like normally, it seems like is would make more sense to keep showing the 'preview' version rather than switching to the 'current' version.