Eliminate ?MEMORY_LIMIT_SCALING and make the ratio at which we page configurable. Note that I have changed the representation from a ratio-of-a-ratio to just a plain ratio (i.e. propertion of total memory, not proportion of the high watermark). I believe this will be easier to understand. Hence also the name vm_memory_paging_watermark, chosen by analogy with vm_memory_high_watermark.
Matthias convinced me to go with ratio-of-a-ratio.
Oops, I forgot that going back to vm_memory_monitor:get_memory_limit() means we can now have a limit of 0.0.
Merged bug25597 into default