Fix T43905: Crash happens when press Create Plane Track

It was only happening on 32bit platforms because of alignment
differences when allocating class.

Now got rid of copy of eigen matricies stored by value in the
residual block which solves aligment issues and should also
give some unmeasurable speedup.

extern/libmv/libmv/multiview/homography.cc

@@ -209,8 +209,8 @@ class HomographySymmetricGeometricCostFunctor {
     return true;
   }
 
-  const Vec2 x_;
-  const Vec2 y_;
+  const Vec2 &x_;
+  const Vec2 &y_;
 };
 
 // Termination checking callback used for homography estimation.