* build.xml: Build speedups:

      - Don't distclean in the updaterRouter target
      - Don't make prepUpdate and prepupdateSmall depend
        on distclean
      - Don't make susimail build always clean
      - Make pkg depend on distclean to be sure
      - Clean out more routerconsole and susidns files in 'ant clean'
      - i2ptunnel, routerconsole, susidns:
        Only build WEB-INF when necessary
      - systray: Only build jar when necessary
      - Don't build i2psnark standalone for the updater target