"extract" script for extraction. Many cases where a custom EXTRACT_CMD
simply copied the distfile into the work directory are no longer
needed. The extract script also hides differences between pax and
tar behind a common command-line interface, so we no longer need code
that's conditional on whether EXTRACT_USING is tar or pax.
MD4 Collision Generation
Faster implementation of techniques described in Cryptanalysis for
Hash Functions MD4 and RIPEMD, by Xiaoyun Wang, et al.
Average runtime on P4 1.6ghz - 5 seconds