* vectorize dot product, copying code from sum.

* make the conj functor vectorizable: it is just identity in real case,
  and complex doesn't use the vectorized path anyway.
* fix bug in Block: a 3x1 block in a 4x4 matrix (all fixed-size)
  should not be vectorizable, since in fixed-size we are assuming
  the size to be a multiple of packet size. (Or would you prefer
  Vector3d to be flagged "packetaccess" even though no packet access
  is possible on vectors of that type?)
* rename:
  isOrtho for vectors ---> isOrthogonal
  isOrtho for matrices ---> isUnitary
* add normalize()
* reimplement normalized with quotient1 functor

doc/snippets/MatrixBase_isUnitary.cpp

@@ -0,0 +1,5 @@
+Matrix3d m = Matrix3d::identity();
+m(0,2) = 1e-4;
+cout << "Here's the matrix m:" << endl << m << endl;
+cout << "m.isUnitary() returns: " << m.isUnitary() << endl;
+cout << "m.isUnitary(1e-3) returns: " << m.isUnitary(1e-3) << endl;