force scanvenge/marksweep in idle gemServers

[dalehenrich]

See the discussion in the mailing list for context, but long story short ... when operating with a large TOC, it is possible that when a gemserver goes idle, a significant amount of toc space will consume real memory that would normally be returned to the os if a mark sweep was run ... @marianopeck finds that the following does a good job of ensuring that idle gems consume the minimum amount of real memory:

"This thread is needed to handle the SigAbort exception, when the primary
 thread is blocked on an accept. Assuming default 60 second
 STN_GEM_ABORT_TIMEOUT, wake up at 30 second intervals."
 [
        | count minutesToForceGemGC |
        count := 0.
        minutesToForceGemGC := 30.
   [ true ] whileTrue: [
                (Delay forSeconds: 30) wait.
                count := count + 1.
                (count \\\ (minutesToForceGemGC * 2)) = 0 ifTrue: [
                        System _generationScavenge_vmMarkSweep.
                        Transcript show: 'Gem GC forced'; cr.
                        count := 0.
                        ].
        ].
 ] forkAt: Processor lowestPriority.

An extra scavenge and marksweep every thirty minutes will add a significant load on the system