[svn-r6952] bugfix tt#1060: add a simple buffer aliasing check to MPI_Allgather

Thanks to Joe Ratterman @ IBM for the bug report.

No reviewer.

src/mpi/coll/allgather.c

@@ -873,6 +873,10 @@ int MPI_Allgather(void *sendbuf, int sendcount, MPI_Datatype sendtype,
             }
 	    MPIR_ERRTEST_USERBUFFER(recvbuf,recvcount,recvtype,mpi_errno);
 
+            /* catch common aliasing cases */
+            if (sendbuf != MPI_IN_PLACE && sendtype == recvtype && recvcount != 0 && sendcount != 0)
+                MPIR_ERRTEST_ALIAS_COLL(sendbuf,recvbuf,mpi_errno);
+
             if (mpi_errno != MPI_SUCCESS) goto fn_fail;
         }
         MPID_END_ERROR_CHECKS;