A list of language constructs that occur in adder_par.c that haven't occurred in previous examples.  Items in this list may or may not require more work before this example passes.

 * If statements
 * include statements
 * External functions (MPI_Init, MPI_send, etc.)
 * Other external definitions  (MPI_DOUBLE, MPI_COMM_WORLD, MPI_STATUS_IGNORE) 
 * Division, Multiplication