- introduce Part and Extract classes, splitting and extending the former

Triangular class
- full meta-unrolling in Part
- move inverseProduct() to MatrixBase
- compilation fix in ProductWIP: introduce a meta-selector to only do
  direct access on types that support it.
- phase out the old Product, remove the WIP_DIRTY stuff.
- misc renaming and fixes

Eigen/src/QR/QR.h

@@ -111,7 +111,7 @@ template<typename MatrixType>
 typename QR<MatrixType>::RMatrixType QR<MatrixType>::matrixR(void) const
 {
   int cols = m_qr.cols();
-  RMatrixType res = m_qr.block(0,0,cols,cols).upperWithNullDiag();
+  RMatrixType res = m_qr.block(0,0,cols,cols).strictlyUpper();
   res.diagonal() = m_norms;
   return res;
 }