Recreate lib/ant from Apache source/binary downloads

Recreate lib/ant from Apache source/binary downloads

- Download Ant 1.6.3 binaries and sources ZIPs from Apache releases
  download server
- Verify expected SHA-1 checksums
- Unpack binary distribution
- Repack main sources into source package as it is checked in now
- Redundantly add JUnit JAR in order to 100% replicate existing
  directory layout
- Move downloads from 'validate' phase to 'generate-resources'
- Unpack/repack phase is 'process-resources'
- Make sure that download, unpack, repack only occur if necessary
  instead of overwriting existing artifacts during each build

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>