Merge branch 'fix/cmake-missing-curly-braces' into 'master'

[cmake] Missing curly braces in include directories

See merge request !43

parallel/CMakeLists.txt

@@ -2,7 +2,7 @@ if(MPI_C_FOUND)
   # we need to deactivate the MPI C++ bindings
   # Maybe dune-common should export them?
   add_definitions(-DENABLE_MPI=1 -DMPICH_SKIP_MPICXX -DMPIPP_H)
-  include_directories("$MPI_DUNE_INCLUDE_PATH")
+  include_directories("${MPI_DUNE_INCLUDE_PATH}")
   set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS ${MPI_DUNE_COMPILE_FLAGS})
  ug_add_dim_libs(parallel OBJECT initparallel.cc) # OBJECT_DIM_LIBS ddd dddif)
 endif()