[Mpi3-ft] Updates to ft chapter

[Darius Buntinas]

I've made some changes we discussed on the phone this morning.  You can find the latest pdf here (or at the bottom of the "Modified run-through stabilization" page on the wiki): 
https://svn.mpi-forum.org/trac/mpi-forum-web/attachment/wiki/ft/run_through_stabilization_2/ft.pdf

Here's a summary of the changes:
 * Changed MPI_ERR_RANK_FAIL_STOP to MPI_ERR_PROC_FAIL_STOP (because a "rank" doesn't fail, a "processes" does)
 * Fixed up usage of rank vs process in the chapter.
 * Removed MPI_COMM_COLLECTIVES_ENABLED function because it returns local version of a global state which is meaningless for applications.
 * Added MPI_COMM_ANY_SOURCE_ENABLED
 * Moved the definition of MPI_COMM_VALIDATE et.al. earlier in the section, and added a new subsection.

Please look over my changes, especially how I rearranged the collectives section for the definition of MPI_COMM_VALIDATE, and let me know if they look OK.

Thanks!
-d