Merge branch 'fix/istlsolverfactorybackend-includes' into 'master'

[solverfactorybackend] add version guard around include

See merge request !1943

dumux/linear/istlsolverfactorybackend.hh

@@ -27,6 +27,8 @@
 #define DUMUX_LINEAR_ISTL_SOLVERFACTORYBACKEND_HH
 
 #include <dune/common/version.hh>
+#if DUNE_VERSION_NEWER_REV(DUNE_ISTL,2,7,1)
+
 #include <dune/common/parallel/mpihelper.hh>
 #include <dune/common/parametertree.hh>
 
@@ -43,8 +45,6 @@
 #include <dumux/linear/solver.hh>
 #include <dumux/linear/parallelhelpers.hh>
 
-#if DUNE_VERSION_NEWER_REV(DUNE_ISTL,2,7,1)
-
 namespace Dumux {
 
 /*!