Many functions are not implemented at all.

Some Point-to-point functions do not work.  Some nonblocking stuff missing.
Make Wait() functions show possible deadlock.

User-defined datatypes do not work.

User-defined MPI_Op's do not work.

MPI_Errhandler do not work.
Could use MPI_ERRORS_ARE_FATAL or MPI_ERRORS_RETURN,
use MPI2 MPI_Comm_set_errhandler to set.

MPI_Cart* do not do the right thing.  More generally, using more
than one communicator does not work reliably, but is not flagged.

make MPI_Wtime more portable.  Can MPI_Wtick be made more accurate?

use dist-hook: or similar to update ChangeLog automagically.

PMPI_* weak symbols.
One public function per file, since they have to be overridable one by one.

nullmpi_conf.h is not always updated correctly.

Use nullmpi_handle_error for all possible errors.
