Refine plane connection by ransac pr

Refine the result of segmentation planes.
Originally, the result of segmentation might be too small, so we need to merge across several small planes.
This patch refines planar coefficients using RANSAC after merging.

Red line is the result before refinement, and blue line is the refined result

![screenshot_from_2014-09-10 15 06 14](https://cloud.githubusercontent.com/assets/40454/4213263/f58c5918-38b1-11e4-8285-aaa999de7f2b.png)