Merge branch 'cl/conditional-config-on-worktree-path' into seen

The [includeIf "condition"] conditional inclusion facility for
configuration files has learned to use the location of worktree
in its condition.

* cl/conditional-config-on-worktree-path:
  config: add "worktree" and "worktree/i" includeIf conditions
  config: refactor include_by_gitdir() into include_by_path()

diff --cc Documentation/config.adoc
Simple merge

diff --cc config.c
Simple merge

diff --cc t/t1305-config-include.sh
Simple merge