malloc probes for Systemtap

[Roland McGrath]

> Let's discuss this separatly. Should we - at this point in time - make 
> any promises about the ABI of probes? Or should we explictely warn users 
> that those might change in the future and are not stable?

When we added the setjmp probes, the decision was that they did not need to
be declared stable, even though GDB was using them.  So it's not very clear
at all.  Let's move this to a different thread, and include at least Tom
Tromey (who decided that GDB should use setjmp probes and that them being
not officially stable was OK).