Debugging output for various layers.  Tightened memory utilization for image layers.  Added distance option for view updates.  Now sorting view updates by priority.  Scene graph manager now enable/disabling rather than recreating.  EAGLView will no longer draw if the app is in background.  This happened in a very few layout cases.
Merge branch 'develop' of git+ssh://github.com/mousebird/WhirlyGlobe into develop