Build generated Kuroko codecs module components

[klange]

Originally reported in kuroko-lang/kuroko#59

We are not building the generated parts of the codecs module.

Likely the best approach to this would be to build them once and then commit them in the repository (possibly in their final location of base/lib/kuroko/codecs/). Building them dynamically requires a more featureful Kuroko interpreter than we have historically been shipping in the Docker build tools, and the scripts also take a while (relative to the rest of our build).

[klange]

dbdata.krk is pretty big; even after gzipping, it increases our ramdisk size by about 1M. Something to consider.

[klange]

With the changes from f840d39, we can now guarantee that the Docker containers have the latest interpreter available. We need to provide the interpreter with a useful KUROKOENV, and then we can use it run the generators:

$ KUROKOPATH=`pwd`/modules/ ../util/local/bin/kuroko  tools/codectools/gen_dbdata.krk
$ KUROKOPATH=`pwd`/modules/ ../util/local/bin/kuroko  tools/codectools/gen_sbenc.krk