Making relevant functions/variables protected

Any functions/variables that could've been made protected have been made so.  However, there are quite a few functions/variables that are still under the public underscore protection that we may want to look at.  This includes:

dataset_getExtent
abstractDrawer._renderArea
absractDrawer._enterData
abstractDrawer._drawStep
elementDrawer._getDrawSelection
abstractInteraction._anchor
abstractScale._typeCoercer
abstractScale._autoDomainIfAutomaticMode
abstractScale._updateExtent
abstractScale._removeExtent
timeScale._tickInterval
dragBoxInteraction._CAN_RESIZE_X
dragBoxInteraction._CAN_RESIZE_Y