Use relative ratio less than epsilon to check zero.

[hongkai-dai]

In ccdVec3PointTriDist2, instead of checking if the triangle area is less than epsilon, we use the ratio (which measures the sine angle) less than epsilon to determine if the triangle area can be used as a denominator. This avoids the problem when CCD incorrectly doesn't trust the projection onto the interior of the triangle, and instead project to the edges of the triangle, causing bad witness point.