Fixing compilation and runtime issues in timing.c.w

[cboneti]

This fixes the issue #11 Besides the compilation errors described in the issue. There was also a runtime error of multiple MPI_Send/Recv being called after MPI_Finalize.

[alehaa]

Is there a reason for renaming the variables?

[cboneti]

Just to differentiate from the structure tag, for clarity. counter.c.w also has a similar approach, the struct tag is "counter" whereas the variable is counters.