starpu-mpi: re-add line which was wrongly deleted

mpi/Makefile.am

@@ -75,7 +75,8 @@ include_HEADERS =					\
 libstarpumpi_la_SOURCES =				\
 	starpu_mpi.c					\
 	starpu_mpi_helper.c				\
-	starpu_mpi_datatype.c
+	starpu_mpi_datatype.c				\
+	starpu_mpi_insert_task.c
 
 
 examplebin_PROGRAMS +=				\