Add Gilles Gouaillardet / RIST to the AUTHORS file
btl/scif: update the size when preparing send fragments

Thanks to Gilles Gouaillardet for catching this.

cmr=v1.8.2:reviewer=jsquyres
Fix memory leak when releasing a communicator created by
MPI_Cart_Create/MPI_Graph_create/MPI_Dist_Graph

Fixes #4581