A build release. The clock is unchanged.

* The build no longer requires JAVA_HOME. A JDK on PATH is enough, which is what an
  ordinary distribution install and the F-Droid build server both provide.
* The APK is now byte-for-byte the same wherever it is built. Zip entries store a local
  date with no timezone, and the dex entry carried the time of the build, so the same
  source used to produce different files on different machines.
