Blender Git Loki

Start migrating away from pat_min and pat_max for markers

This starts converting markers in the movie clip editor / 2D
tracker from using pat_min and pat_max notation to using the
a more general, 4-corner representation. There is still
considerable porting work to do; in particular:

- The preview widget does not respect the new
representation
- The corners cannot yet be edited individually.
- The clamping does not do the right thing for general
corners; e.g. detecting a convex quad.
- The tracking code in Blender does not actually invoke the
corner tracking version of libmv's tracking API.

Next steps:

- Convert libmv's legacy ESM tracker and brute tracker to
work under the new TrackRegion() API.
- Make Blender use the new TrackRegion() API; this will
allow real planar tracking tests.
- Everything else (UI, etc).

This patch is mostly the work of Sergey Sharybin.