Blender Git Loki

GPencil Eraser: Operates on all visible + editable layers instead of active only

The GPencil eraser now operates on all visible and editable layers, instead of
only operating on the active layer. There was really no reason why it needed to
only consider the active layer, as doing so only made it confusing for the user when
the strokes they were trying to erase wouldn't be affected. Besides, if you really
needed to restrict the eraser to working on a particular layer, you could just
lock all the others (which is now very easy with the new operators)