All three all-to-all scatter/gather routines (MPI_Alltoall,
MPI_Alltoallv, and MPI_Alltoallw) now accept MPI_IN_PLACE as a valid
sendbuf argument.

This is an implementation of MPI Forum ticket #31 for MPI-2.2
compliance.  See the following URL for more information:

https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/31

No reviewer.

[svn-r3177] Switch to the new macro for the global thread critical section (most of this is an automated change, tested against the MPICH2 test suite)