Merge branch 'rs/pop-commit' into maint

Code simplification.

* rs/pop-commit:
use pop_commit() for consuming the first entry of a struct commit_list

diff --cc builtin/fmt-merge-msg.c
Simple merge

diff --cc builtin/merge.c
Simple merge

diff --cc builtin/reflog.c
Simple merge

diff --cc builtin/show-branch.c
Simple merge

diff --cc commit.c
Simple merge

diff --cc revision.c
Simple merge

diff --cc shallow.c
Simple merge