Added a --cfg="smpi/simulation_computation" to smpirun. The default
value is "yes", meaning that SMPI will benchmark computational parts
of the simulation application and simulate them using smpi_execute(), as
it's always been done in the past.
Disabling the simulation of computation is useful when smpirunning an "application"
that is in fact doing a "live replay" of another MPI app (e.g., ScalaTrace's replay tool, various on-line simulators that run an app at scale). In this case the computation due to the replay logic
should be be simulated by SMPI.
For the time being, for smpirunning such an "application", the approach is:
1. use --cfg="smpi/simulation_computation:no"
2. add calls to smpi_execute() in the "application"
