Merge branch 'fc/completion'

In addition to a user visible change to offer more options to cherry-pick, generally cleans up and simplifies the code. * fc/completion: completion: small optimization completion: inline __gitcomp_1 to its sole callsite completion: get rid of compgen completion: add __gitcomp_nl tests completion: add new __gitcompadd helper completion: get rid of empty COMPREPLY assignments completion: trivial test improvement completion: add more cherry-pick options