v2.0.2

Ship a USB install bundle; load BOOTCLASSPATH for the probe

The release zip is the package itself. Extracted onto a USB drive, its
NEMESIS.data has no type=, so the USB handler reports "Invalid package
descriptor". build.sh now also writes media.codecs--usb.zip in the
layout of NEMESIS's own release zips: a type=install descriptor plus
packages/media.codecs.zip.

USB installs run from the usb-handler service, which may not pass init's
BOOTCLASSPATH down to the hooks, and app_process needs it. run_probe now
loads it from /init.environ.rc when it's unset.

Bump to 2.0.2.