See COPYING file in tarball. This contains a list of terms I to IV, as follows: I. BSD-4 (only with different copyright holder) II. ZLIB III. "... placed into the Public Domain, do with it what you will." IV. concerns the files sha1.{cc,h} only: "The Bitzi Corporation places its portion of these labelled works into the public domain, disclaiming all rights granted us by copyright law" (plus some verbose fluff) In summary, LICENSE="BSD-4 ZLIB public-domain" should be fine.
Thanks for the report. It is fixed.