SimGrid 3.11.1

Updated SimGrid from 3.9 to 3.11.1. Neither version compiles under OS X
10.8…
SimGrid 3.11.1 upgrade

Successfully installed SimGrid 3.11.1 on OS X 10.8 and 10.9…
boost:optional

Boost is an optional dependency for 10.9…
Boost != optional

It is needed under all versions of OS X I’ve tested (10.9 and 10.8).
There was something wrong with my syntax in the previous commit…
simgrid: add 3.11.1 bottle.