Merge branch 'as/dir-c-cleanup'

Merge branch 'as/dir-c-cleanup'

Refactor and generally clean up the directory traversal API
implementation.

* as/dir-c-cleanup:
  dir.c: rename free_excludes() to clear_exclude_list()
  dir.c: refactor is_path_excluded()
  dir.c: refactor is_excluded()
  dir.c: refactor is_excluded_from_list()
  dir.c: rename excluded() to is_excluded()
  dir.c: rename excluded_from_list() to is_excluded_from_list()
  dir.c: rename path_excluded() to is_path_excluded()
  dir.c: rename cryptic 'which' variable to more consistent name
  Improve documentation and comments regarding directory traversal API
  api-directory-listing.txt: update to match code