Declare a need to know if BOOST is available

Note that the variable HAVE_DUNE_BOOST is not set by FindBoost,
but by OpmAliases.

cmake/Modules/Finddune-common.cmake

@@ -50,6 +50,7 @@ int main (void) {
   HAVE_ARRAY;
   HAVE_BOOST_MAKE_SHARED_HPP;
   HAVE_BOOST_SHARED_PTR_HPP;
+  HAVE_DUNE_BOOST;
   HAVE_GMP;
   HAVE_MAKE_SHARED;
   HAVE_MPI;

cmake/Modules/OpmAliases.cmake

@@ -9,6 +9,7 @@ function (set_aliases)
   # are separated by space
   set (aliases
 	"HAVE_UMFPACK             HAVE_SUITESPARSE_UMFPACK_H"
+	"HAVE_DUNE_BOOST          HAVE_BOOST"
 	)
   foreach (alias IN LISTS aliases)
 	# convert entry "X Y" into a list "X;Y", then pick apart