CI speed improvements for FreeBSD

Hi,

Here are a couple of changes that got FreeBSD down to 4:29 total, 2:40
in test_world in my last run (over 2x speedup), using a RAM disk
backed by a swap partition, and more CPUs.  It's still a regular UFS
file system but FreeBSD is not as good at avoiding I/O around short
lived files and directories as Linux: it can get hung up on a bunch of
synchronous I/O, and also flushes disk caches for those writes,
without an off switch.

I don't know about Windows, but I suspect the same applies there, ie
synchronous I/O blocking system calls around our blizzard of file
creations and unlinks.  Anyone know how to try it?