Merge branch 'en/fill-directory-exponential'

The directory traversal code had redundant recursive calls which
made its performance characteristics exponential with respect to
the depth of the tree, which was corrected.

* en/fill-directory-exponential:
  completion: fix 'git add' on paths under an untracked directory
  Fix error-prone fill_directory() API; make it only return matches
  dir: replace double pathspec matching with single in treat_directory()
  dir: include DIR_KEEP_UNTRACKED_CONTENTS handling in treat_directory()
  dir: replace exponential algorithm with a linear one
  dir: refactor treat_directory to clarify control flow
  dir: fix confusion based on variable tense
  dir: fix broken comment
  dir: consolidate treat_path() and treat_one_path()
  dir: fix simple typo in comment
  t3000: add more testcases testing a variety of ls-files issues
  t7063: more thorough status checking

diff --cc builtin/clean.c
Simple merge

diff --cc builtin/grep.c
Simple merge

diff --cc builtin/stash.c
Simple merge

diff --cc contrib/completion/git-completion.bash
Simple merge

diff --cc dir.c
Simple merge

diff --cc t/t7063-status-untracked-cache.sh
Simple merge

diff --cc t/t9902-completion.sh
Simple merge