#7 multiple CPU usage in RooAbsPdf::generate

[Gerhard Raven]

The bottleneck for what I happen to be doing is in toy
generation (and
to be more precise, finding the maximum value in the
accept-reject
generation) and given that I have access to a dual-CPU
machine, it
would be nice if RooAbsPdf::generate would recognize
NumCPU(n),
and spread the use over n CPUs. Note that the difficult
part will be to
make sure that the events generated are independent of
whether NumCPU is specified or not....