* revert the previous interface change in solveTriangular (pointer vs reference)

* remove the cast operators in the Geometry module: they are replaced by constructors
  and new operator= in Matrix
* extended the operations supported by Rotation2D
* rewrite in solveTriangular:
  - merge the Upper and Lower specializations
  - big optimization of the path for row-major triangular matrices

Eigen/src/Core/Matrix.h

@@ -363,6 +363,13 @@ class Matrix : public MatrixBase<Matrix<_Scalar, _Rows, _Cols, _MaxRows, _MaxCol
       else
         this->Base::swap(other);
     }
+
+/////////// Geometry module ///////////
+
+    explicit Matrix(const Quaternion<Scalar>& q);
+    Matrix& operator=(const Quaternion<Scalar>& q);
+    explicit Matrix(const AngleAxis<Scalar>& aa);
+    Matrix& operator=(const AngleAxis<Scalar>& aa);
 };
 
 /** \defgroup matrixtypedefs Global matrix typedefs