Blender Git Loki

Made View2D drag zoom behave in the same way as zoom in 3d viewport

Initially issue was caused by opposite MMB-Drag zoom direction in nodes editor.

Made it so MMB-Drag in negative axis direction (down for Y axis and left for
X axis) would zoom in, moving in opposite direction will zoom out.

This could kind of break muscule memory, but after discussion with Campbell
decided it's not so big a problem -- seems users weren't related on direction
of zoom in and just waved mouse around until zoom is correct. And now muscule
memory should even be a bit better -- drag zoom is unified between different
areas.