Documentation for functions inside tracking.c

Additional changes:

- Cleaned up sources to reduce mess in some
  big functions.
- Removed unused function from libmv c-api.
- Made functions naming more consistent.
- Use bool for internal stuff in tracking.c.

Shall be no functional changes :)

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56715 954f8c5b-7b00-dc11-b283-0030488c597c
Refine markers position operator

This operator will run a tracker from previous
keyframe to current frame for all selected markers.
Current markers positions are considering initial
position guess which could be updated by a tracker
for better match.

Useful in cases when feature disappears from the
frame and then appears again. Usage in this case
is the following:

- When feature point re-appeared on frame, manully
  place marker on it.
- Use Refine Markers operation (which is in Track
  panel) to allow tracker to find a better match.

Depending on direction of tracking use either
Forwards or Backwards refining. It's easy: if
trackign happens forwards, use Refine Frowards,
otherwise use Refine Backwards :)

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56716 954f8c5b-7b00-dc11-b283-0030488c597c