Merge branch 'rs/resolve-ref-optional-result'

Code clean-up.

* rs/resolve-ref-optional-result:
refs: pass NULL to resolve_refdup() if hash is not needed
refs: pass NULL to refs_resolve_refdup() if hash is not needed

diff --cc builtin/checkout.c
Simple merge

diff --cc builtin/receive-pack.c
Simple merge

diff --cc refs/files-backend.c
Simple merge

diff --cc wt-status.c
Simple merge