Jacobi improvements:   * add fixed-size vectorized path   * add missing restrict keywords   * use innerStride()   * allow vectorization even if innerStride()>1, if PacketSize==1     (think of the case of rows of std::complex<double>)
Jacobi improvements:
  * add fixed-size vectorized path
  * add missing restrict keywords
  * use innerStride()
  * allow vectorization even if innerStride()>1, if PacketSize==1
    (think of the case of rows of std::complex<double>)

madlib/eigen,madlib/eigen,madlib/eigen,madlib/eigen