A few of upstream's dual-licensed files carry code from other projects
under MIT or BSD terms. The fork redistributes it, so their licenses
require the notices to travel with it. THIRD-PARTY.md reproduces them.
strip.py now reads the stripped tree's comments for another copyright
holder, another license, or a note that code came from somewhere else, and
names any file THIRD-PARTY.md doesn't cover. It reports, never fails: the
notice goes in with the merge that brings the release in.
On v0.16.22 it finds 14 files, all of them covered. The rest of the report
is byte-for-byte what the committed one says, so the scan disturbs nothing
it already did.
