To make circle select allow pass-through for view events, several issues have to be
tackled.
1) other modal ops run on top (border select),
2) middlemouse is used now
3) and what for tablet/trackpad or people without middlemouse?
The MMB deselection for border/circle is not optimal now... needs rethinking this.
Better would be to check on non-persistant-modality for circle, to start with gesture style
event like lasso or border can do now.