lua.wetgenes.tardis.m4.v3
v3 = m4:v3(n)
Extract and return a "useful" v3 from an m4 matrix. The first vector is the x axis, then y axis , then z axis and finally transform.
If n is not given or not a known value then we return the 4th vector which is the "opengl" transform as that is the most useful v3 part of an m4.