Suggestion from Andreas Schäfer: we really only need sqrt(freeprocs)

primes.  This considerably reduces the computational load when
freeprocs is large.

cmr=v1.7.5:reviewer=hjelmn:subject=MPI_Dims_create optimization

This commit was SVN r30539.

ompi/mpi/c/dims_create.c

@@ -11,6 +11,7 @@
  *                         All rights reserved.
  * Copyright (c) 2012      Los Alamos National Security, LLC.  All rights
  *                         reserved. 
+ * Copyright (c) 2014 Cisco Systems, Inc.  All rights reserved.
  * $COPYRIGHT$
  * 
  * Additional copyrights may follow
@@ -109,7 +110,7 @@ int MPI_Dims_create(int nnodes, int ndims, int dims[])
     }
 
     /* Compute the relevant prime numbers for factoring */
-    if (MPI_SUCCESS != (err = getprimes(freeprocs, &nprimes, &primes))) {
+    if (MPI_SUCCESS != (err = getprimes(sqrt(freeprocs), &nprimes, &primes))) {
        return OMPI_ERRHANDLER_INVOKE(MPI_COMM_WORLD, err,
                                      FUNC_NAME);
     }