Warn when map has fallThrough != true

This PR suggests to issue a warning in the developer console when a map is being used that doesn't configure `fallThrough:true`.

In my experience this an easy oversight and has caused a lot of headaches, see e.g.: http://osgeo-org.1560.x6.nabble.com/OpenLayers-2-13-floating-components-resize-not-working-td5151955.html

Please review.