Motion Path drawing tweaks and fixes

* Green (current frame) color now extends to the segments on either side of the
current frame point. This is so that the path is more visible (especially on the
black/dark side), as those segments were prone to being interpolated such that
they became invisible

* Added padding for frame number strings so that they do not overlap the dots
anymore

* Fixed off-by-one error, which meant that the frame number for the first frame
step (white dot) didn't get shown


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53643 954f8c5b-7b00-dc11-b283-0030488c597c