I've implemented the handling of the trackpad 2-fingers gestures :

- 2 fingers scroll (MOUSEPAN / GHOST_kTrackpadEventScroll event) pans the view
- 2 fingers pinch (MOUSEZOOM / GHOST_kTrackpadEventMagnify event) zooms the view
And in 3D view:
- alt + 2 fingers scroll rotates the view
- 2 fingers rotation (MOUSEROTATE / GHOST_kTrackpadEventRotate) rotates the view around the axis orthogonal to the screen (the 3rd axis !)

The implementation uses a new GHOST event type: GHOST_kEventTrackpad, that is then dispatch as Blender MOUSEPAN, MOUSEZOOM or MOUSEROTATE events.

This is currently fully implemented for OSX (GHOST Cocoa fires the new events), but there must be some PC laptops with similar features that'll take advantage of this... Linux/Win users, can you confirm ? (I remember using a laptop with the 2D scroll features on its trackpad).

In Ghost, I've currently implemented an auto-detection of the source peripheral, so that a regular mouse still sends MOUSEWHEEL events.
Apple special mice behave like trackpad (not configurable from documented API), so the mighty mouse trackball sends 2D scroll events. And the magic mouse touch gestures must be like trackpad's.