* Big change in Block and Map:

- added a MapBase base xpr on top of which Map and the specialization
    of Block are implemented
  - MapBase forces both aligned loads (and aligned stores, see below) in expressions
    such as "x.block(...) += other_expr"
* Significant vectorization improvement:
 - added a AlignedBit flag meaning the first coeff/packet is aligned,
   this allows to not generate extra code to deal with the first unaligned part
 - removed all unaligned stores when no unrolling
 - removed unaligned loads in Sum when the input as the DirectAccessBit flag
* Some code simplification in CacheFriendly product
* Some minor documentation improvements

Eigen/src/Geometry/Quaternion.h

@@ -105,8 +105,11 @@ public:
 
   /** Constructs and initializes the quaternion \f$ w+xi+yj+zk \f$ from
     * its four coefficients \a w, \a x, \a y and \a z.
+    * 
+    * \warning Note the order of the arguments: the real \a w coefficient first,
+    * while internally the coefficients are stored in the following order:
+    * [\c x, \c y, \c z, \c w]
     */
-  // FIXME what is the prefered order: w x,y,z or x,y,z,w ?
   inline Quaternion(Scalar w, Scalar x, Scalar y, Scalar z)
   { m_coeffs << x, y, z, w; }
 
@@ -313,8 +316,8 @@ inline Quaternion<Scalar>& Quaternion<Scalar>::setFromTwoVectors(const MatrixBas
 }
 
 /** \returns the multiplicative inverse of \c *this
-  * Note that in most cases, i.e., if you simply want the opposite
-  * rotation, it is enough to use the conjugate.
+  * Note that in most cases, i.e., if you simply want the opposite rotation,
+  * and/or the quaternion is normalized, then it is enough to use the conjugate.
   *
   * \sa Quaternion::conjugate()
   */