[umfpack] Factorization extraction, make colcomp public

Cherry-picked changes, left out white-space changes,
from 857fdd91dcea7af2ab5f1c1147a59a187cb253db
and 8c21e316e4b72b38972b0c1a93254171566979c6

Signed-off-by: Christoph Grüninger <gruenich@dune-project.org>

dune/istl/umfpack.hh

@@ -433,6 +433,24 @@ namespace Dune {
         UMF_Control[UMFPACK_PRL] = 4;
     }
 
+    /**
+     * @brief Return the matrix factorization.
+     * @warning It is up to the user to keep consistency.
+     */
+    void* getFactorization()
+    {
+      return UMF_Numeric;
+    }
+
+    /**
+     * @brief Return the column compress matrix from UMFPack.
+     * @warning It is up to the user to keep consistency.
+     */
+    UMFPackMatrix& getInternalMatrix()
+    {
+      return umfpackMatrix_;
+    }
+
     /**
      * @brief free allocated space.
      * @warning later calling apply will result in an error.
@@ -505,8 +523,6 @@ namespace Dune {
       }
     }
 
-    UMFPackMatrix& getInternalMatrix() { return umfpackMatrix_; }
-
     UMFPackMatrix umfpackMatrix_;
     bool matrixIsLoaded_;
     int verbosity_;