ruler snap adjustments
- when in wireframe mode: don't snap to faces, instead snap to the closest edge/vertex.
- when not in wireframe mode: snap to the front-most element (was a problem that it could snap to an edge/vert behind the face)
- reduce the distance for selecting ruler points, was too easy to accidentally drag a ruler.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56287 954f8c5b-7b00-dc11-b283-0030488c597c