Merge branch 'rs/cocci'

Code clean-up with help from coccinelle tool continues.

* rs/cocci:
  coccicheck: make transformation for strbuf_addf(sb, "...") more precise
  use strbuf_add_unique_abbrev() for adding short hashes, part 2
  use strbuf_addstr() instead of strbuf_addf() with "%s", part 2
  gitignore: ignore output files of coccicheck make target
