Build everything back to 2014.01

Kind of annoyed that we cannot bisect sometimes because the change is too old. It is surprising how often this happens.

In issue #23 it was noticed that lrz, although being relatively slow, does an amazing job compressing several builds at the same time. This means that for long-term storage we can put 50 (or so) builds together, and this way store most of them for free (in terms of storage). Yes, all operations with these builds will be slower, but I guess anyone can wait a second or two if they're trying to access something that old.

These changes are required:

• build-exists should try to find .zst archives first, and if this fails try to find the build elsewhere. We will need some sort of lookup mechanism for finding the right file.
• These two lines changed accordingly. Make sure that during this process we are not saving builds that are not required.
• Change build.p6 so that it can figure out that 50 consequent .zst archives can be recompressed with .lrz instead.

Start with build-exists in Whateverable.pm6, especially the linked lines 124 and 172-173, and read issue #23 for the compression context. Then inspect build.p6 to understand how builds are selected and stored. Done means older builds can locate .zst archives, avoid retaining unnecessary builds, and identify groups of 50 consecutive .zst archives for .lrz recompression.