Fossil SCM 2.1 released with SHA3-256 support and graceful upgrading

Fossil now comes with a configurable hash use policy, and by default uses SHA3 once peers start:

> Beginning with Fossil 2.1, the default hash policy for legacy repositories changed to "auto". That means Fossil 2.1 will continue to generate only SHA1 hashes until it encounters one artifact with a SHA3 hash. Once a single SHA3 hash is seen, Fossil automatically switches to "sha3" mode and thereafter generates only SHA3 hashes.