Rewrite the description of the CPU throttle

[Ageless]

At this moment the CPU Usage throttle is a misnomer, as it says to "use at most x% of CPU time", while it doesn't throttle the CPU time and certainly not a percentage of it.

What it does is throttle BOINC's use of the CPU, suspending the science application so many times per 10 seconds, as given in by the percentage number. Yet a task taking 40 CPU minutes will still take 40 CPU minutes when throttled at 50%. Its wall clock time will go up to double that or more.

Users are also expecting that if they insert a percentage, that that is the maximum their CPU will run at in terms of CPU cycles. Since it doesn't, a better description of the throttling could help bring things on track.

With the help of ​this thread on the Seti forums, we may have come up with a solution. As posted by Odysseus:

FWIW it would make the most sense to me if the whole thing were to be inverted:

Reduce CPU usage by: [default=0] percent
_{Enforced by version 5.6+
(Pauses processing every few seconds to improve cooling in portable or compact computers.)}

Something like that, anyway. I imagine the preference form could easily convert the percentage back to the usual format (and vice versa when displaying the current setting) so as to avoid having to make changes to the implementation in the CC."

This does mean that the default isn't showing as 100%, but as zero. We also get rid of the mentioning of the CPU time. And there could also be a hyperlink added going off to the Wiki page that shows how this throttling works. (Not existing yet)

[Nicolas]

Reformat as quote.