Merge branch 'rs/code-cleaning'

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