bugfix + mpi cleanup

remove usage of cpp MPI interface. now I'm gonna need to debug this for
the intel compiler...

src/fftwf_tools.cpp

@@ -167,7 +167,8 @@ fftwf_plan plan_transpose(
     howmany_dims[1].os = rows;
     const int howmany_rank = sizeof(howmany_dims)/sizeof(howmany_dims[0]);
 
-    return fftw_plan_guru_r2r(/*rank*/0, /*dims*/NULL,
+    return fftwf_plan_guru_r2r(
+            /*rank*/0, /*dims*/NULL,
             howmany_rank, howmany_dims,
             in, out, /*kind*/NULL, flags);
 }

src/field_descriptor.cpp

@@ -86,11 +86,12 @@ int field_descriptor::read(
     MPI_Info_create(&info);
     MPI_File f;
 
-    f = MPI::File::Open(
+    MPI_File_open(
             this->comm,
             fname,
             MPI_MODE_RDONLY,
-            info);
+            info,
+            &f);
     MPI_File_set_view(
             f,
             0,
@@ -117,11 +118,12 @@ int field_descriptor::write(
     MPI_Info_create(&info);
     MPI_File f;
 
-    f = MPI::File::Open(
+    MPI_File_open(
             this->comm,
             fname,
             MPI_MODE_CREATE | MPI_MODE_WRONLY,
-            info);
+            info,
+            &f);
     MPI_File_set_view(
             f,
             0,
@@ -147,7 +149,6 @@ int field_descriptor::transpose(
     // IMPORTANT NOTE:
     // for 3D transposition, the input data is messed up
     fftwf_plan tplan;
-    ptrdiff_t dim1;
     if (this->ndims == 3)
     {
         // transpose the two local dimensions 1 and 2