Feature Requests: load/swap maximums

[breakone9r]

Add option to "Do not start new builder(s) if load is above:" and default to = numcores.

Also a similar option to not start new builders if swap % is above a certain % to help prevent OOM kills from occuring during builds.

This will allow us to better utilize hardware without worry of overdoing it, by setting builder# to, say 8, and jobs-per-builder to, say 5.. on a 16 core CPU, and keep load fairly close to 16 after the initial jump to 40, by just pausing builders until load drops a bit...

This should satisfy the "redistribute cores" feature request, which is harder to do than it would first appear.

[jrmarino]

an interesting suggestion that should not be that difficult technically to accomplish although it is a new feature (where synth is essentially in bug fix maintenance mode)