Merge branch 'rs/code-cleaning'

* rs/code-cleaning:
fsck: simplify fsck_commit_buffer() by using commit_list_count()
commit: use commit_list_append() instead of duplicating its code
merge: simplify merge_trivial() by using commit_list_append()
use strbuf_addch for adding single characters
use strbuf_addbuf for adding strbufs

diff --cc builtin/merge.c
Simple merge

diff --cc commit.c
Simple merge

diff --cc merge-recursive.c
Simple merge

diff --cc pretty.c
Simple merge

diff --cc rerere.c
Simple merge