fix bug 406: Using OpenMP and Eigen causes infinite loop/deadlock (transplanted from 8b1ca56a7cf05183dc0958f155f8e8a1ff9ff97c)
fix bug 406: Using OpenMP and Eigen causes infinite loop/deadlock
(transplanted from 8b1ca56a7cf05183dc0958f155f8e8a1ff9ff97c)

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