Decrease the GROW_FACTOR in Refine to be less depend on white border

This fix #22.

Unit-tests claim 3 new false negative, but 4 new true positive
and 4 new false negative, but 3 new true positive with LSD_EXPERIMENTAL
Added test image for issue #22
Merge pull request #23 from severin-lemaignan/snowwhite

Decrease the GROW_FACTOR in Refine to be less depend on white border