Test if argument is a homogeneous transformation
ishomog(T) ishomog(T, "valid")
ISHOMOG(T) is true (1) if the argument T is of dimension 4x4 or 4x4xN, else false (0).
ISHOMOG(T, 'valid') as above, but also checks the validity of the rotation matrix.
The first form is a fast, but incomplete, test for a transform in SE(3)
Does not work for the SE(2) case