Merge branch 'fix-memory-leak-in-cholmod-solver' into 'master'

Fix memory leak in the CHOLMOD wrapper code

See merge request !602

dune/istl/cholmod.hh

@@ -461,6 +461,10 @@ public:
 
     });
 
+    // Remove old factor that may be left over from a previous run
+    if (L_)
+      CholmodMethod::free_factor(&L_, &c_);
+
     // Now analyse the pattern and optimal row order
     L_ = CholmodMethod::analyze(M.get(), &c_);