Fix inconsistent behavior of minkmp/pm_ia/ea for empty results

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Make minkmp_ia/ea, minkpm_ia/ea return empty ellipsoidal arrays of proper size 
(size depends on dirMat) instead of empty double arrays

Right now the behavior is inconsistent:

>> ellipsoid(zeros(2)).minkmp_ia(ellipsoid(eye(2)),ellipsoid(eye(2)),[1;0])

ans =

     []

>> ellipsoid(zeros(2)).minkmp_ea(ellipsoid(eye(2)),ellipsoid(eye(2)),[1;0])

ans =

     []

>> res=ellipsoid(zeros(2)).minkpm_ia(ellipsoid(eye(2)),[1;0])

-------ellipsoid object-------
Properties:
   |    
   |-- actualClass : 'ellipsoid'
   |--------- size : [0 0]

Fields (name, type, description):
    Q    double    Ellipsoid shape matrix.
    q    double    Ellipsoid center vector.

Data: 
[Empty array]
>> size(res)

ans =

     0     0

Original issue reported on code.google.com by heartofm...@gmail.com on 24 Dec 2013 at 12:02