* #define EIGEN_NDEBUG now also disables asserts. Useful

to disable eigen's asserts without disabling one's own program's
  asserts. Notice that Eigen code should now use ei_assert()
  instead of assert().
* Remove findBiggestCoeff() as it's now almost redundant.
* Improve echelon.cpp: inner for loop replaced by xprs.
* remove useless "(*this)." here and there. I think they were
  first introduced by automatic search&replace.
* fix compilation in Visitor.h (issue triggered by echelon.cpp)
* improve comment on swap().

Eigen/src/Core/DiagonalMatrix.h

@@ -60,7 +60,7 @@ class DiagonalMatrix : ei_no_assignment_operator,
 
     DiagonalMatrix(const CoeffsVectorType& coeffs) : m_coeffs(coeffs)
     {
-      assert(CoeffsVectorType::IsVectorAtCompileTime
+      ei_assert(CoeffsVectorType::IsVectorAtCompileTime
           && coeffs.size() > 0);
     }