[CoinUtils] User and System time in CoinCpuTime

[Lou Hafer]

Giacomo,

	Thanks for pursuing this. It's nice to know it's not a cbc bug :-)

	On the other hand, if user code is executing and the user time is not
increasing, that sounds like a bug within Linux. It would be useful to
know if you see the same behaviour on other platforms.

	Coming at this from another direction, is it a bug or just a deficiency
in CoinCpuTime, as you suggest. Is this a failure to correctly account
for user time, or is your code really spending all its time executing
system tasks?

	I don't know the reason for the original decision to not include system
time. Someone else will have to speak to that. Speculation would be that
user time accounts for the cost of your code, while system time
potentially includes costs attributable to other code running on the
system and interrupting the continuous execution of your code.

						Lou