PR#19006: use the pkgsrc libjpeg instead of a local copy, and patch a bug in
the serial device file descriptor handling.
Also up the emulated "CPU idle" delay from 10ms to 100ms. For some reason the
former saturates the CPU (on a Celeron 700 system), but with the latter the
program idles at near 0%. This patch is probably not required for native
threads. Mileage may vary...