various work on the Sparse module:

* added some glue to Eigen/Core (SparseBit, ei_eval, Matrix)
* add two new sparse matrix types:
   HashMatrix: based on std::map (for random writes)
   LinkedVectorMatrix: array of linked vectors
   (for outer coherent writes, e.g. to transpose a matrix)
* add a SparseSetter class to easily set/update any kind of matrices, e.g.:
   { SparseSetter<MatrixType,RandomAccessPattern> wrapper(mymatrix);
     for (...) wrapper->coeffRef(rand(),rand()) = rand(); }
* automatic shallow copy for RValue
* and a lot of mess !
plus:
* remove the remaining ArrayBit related stuff
* don't use alloca in product for very large memory allocation

Eigen/Sparse

@@ -4,12 +4,20 @@
 #include "Core"
 #include <vector>
 #include <map>
+#include <stdlib.h>
+#include <string.h>
 
 namespace Eigen {
 
+#include "src/Sparse/SparseUtil.h"
+#include "src/Sparse/SparseMatrixBase.h"
+#include "src/Sparse/SparseProduct.h"
 #include "src/Sparse/SparseArray.h"
 #include "src/Sparse/SparseMatrix.h"
+#include "src/Sparse/HashMatrix.h"
+#include "src/Sparse/LinkedVectorMatrix.h"
 #include "src/Sparse/CoreIterators.h"
+#include "src/Sparse/SparseSetter.h"
 
 } // namespace Eigen