Store the value of token(partition_key) in content_by_* table, instead of three hashes.
That's a big win in terms of disk space, and shouldn't affect performance
negatively (there's only an extra query in content_add
on sha1/sha1_git collisions)
Resolves #2304 (closed).
When this diff is accepted, I'll do a similar one for skipped_content.
Migrated from D2796 (view on Phabricator)