Adjusting the operation of "drawing" parameter in "modify" and "point" callbacks.

This corresponds to bug http://trac.osgeo.org/openlayers/ticket/3319 and the desirability of distinguishing the first point added to a sketch as is discussed in http://osgeo-org.1560.n6.nabble.com/2-11-SketchStarted-td4550864.html.