
 * Hang on make check on Carsten's laptop.
   32-bit Ubuntu Hardy Heron, mpich-mpd-bin 1.2.7-8, mpichboot
   p4est revision e62f33bdd315adf0b7743bc8346800c62d5bb3c6
   configure CFLAGS=-Wall -g -O0 -rdynamic --enable-debug --enable-mpi \
      --enable-stats --with-lint --without-blas
   mpirun -np 2 test/p8est_test_balance
      hangs in the first call to p4est_balance.
   Commenting out balance_response and changing
      p4est_quadrant_checksum into sc_array_checksum resolves the hang.
   The hang occurs intermittently when balance_response is prepended with

   for (zz = 0; zz < 10000; ++zz) {
     sc_array_push (&peer->send_second);
   }
   usleep (200 * 1000 * (1 - p4est->mpirank));
   return;

   So the cause is not inside the balance_response function.
   Seems more like a timings issue / race condition.
