Changes since 3.9-4:

VM:

  Check for and use nanosleep() on all platforms.  This prevents the
  VM consuming 100% CPU on some platforms due to small (1ms) timeouts
  in ioRelinquishProcessor() coming from the idle process.

  Reset interruptCheckCounter at the end of ioRelinquishProcessor to
  ensure input semaphore is signalled promptly after events.

Plugins:

  Added Balloon3DEngine (aka Squeak3D) plugin and bundled it.

  Made UUIDPlugin external to contain damage from missing or
  uncooperative libuuid.