Fix wrong inclusion of local header, use "" instead of <>.

This caused build errors with CMake.

dune/istl/test/inverseoperator2prectest.cc

@@ -8,7 +8,7 @@
 #include<dune/istl/operators.hh>
 #include <dune/common/fmatrix.hh>
 #include <dune/common/fvector.hh>
-#include <laplacian.hh>
+#include "laplacian.hh"
 
 int main(int argc, char** argv)
 {

dune/istl/test/mv.cc

@@ -5,8 +5,8 @@
 #include <dune/istl/operators.hh>
 #include <dune/common/fmatrix.hh>
 #include <dune/common/fvector.hh>
-#include <laplacian.hh>
 #include <dune/common/timer.hh>
+#include "laplacian.hh"
 
 int main(int argc, char** argv)
 {

dune/istl/test/overlappingschwarztest.cc

@@ -6,7 +6,7 @@
 #include <dune/istl/operators.hh>
 #include <dune/common/fmatrix.hh>
 #include <dune/common/fvector.hh>
-#include <laplacian.hh>
+#include "laplacian.hh"
 #include <dune/common/timer.hh>
 #include <dune/common/sllist.hh>
 #include <dune/istl/overlappingschwarz.hh>

dune/istl/test/solvertest.cc

@@ -6,11 +6,10 @@
 #include <dune/istl/operators.hh>
 #include <dune/common/fmatrix.hh>
 #include <dune/common/fvector.hh>
-#include <laplacian.hh>
 #include <dune/common/timer.hh>
-#include <dune/common/sllist.hh>
 #include <dune/istl/overlappingschwarz.hh>
 #include <dune/istl/solvers.hh>
+#include "laplacian.hh"
 
 #include <iterator>