* Cancellation of requests
Currently, cancellation of requests is implemented in the module
itself but needs to be propagated at the ADI level.
The code snipets are included in mx_cancel.c.
However, since MX does not support the cancellation of send requests,
it's unlikely that the MX module will.
Note that for recv request cancellation, the VC is need only to find 
the module function. It's therefore MPI_ANY_SOURCE ready.

* On demand connections
Currently, all connections are established on start-up. Some framework
for on-demand connection is implemented but not yet functionnal.

* Maximum tag length.
Currently, the MX module only supports tags that are at most 31-bits long.
Support for full, 32-bits tags is implemented but some work need to be
done at higher level. The current fix is the following :
1- Uncomment the /* #define USE_CTXT_AS_MARK  */ line in the mx_impl.h file 
2- Replace line 439 in the  src/mpi/comm/commutil.c file : 
   	   context_mask[0] = 0xFFFFFFF8;
   with the following code: 
     	   context_mask[0] = 0xFFFFFFF0;

