callout patch #2 - make callouts per-cpu and MP safe.

[Matthew Dillon]

:Can you also add a flag and an INVARIANT check to ensure that timers
:are indeed correctly initialized? Most code does a bzero or uses default
:zeroing, so we should be able to catch those easily.
:
:Joerg

    Yes, that's a good idea.  I'll add a mandatory flag which callout_init()
    always sets.  but for now we will just printf() if a timer is found to
    not have been properly initialized.

					-Matt
					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>