Merge branch 'vd/sparse-clean-etc'

"git update-index", "git checkout-index", and "git clean" are
taught to work better with the sparse checkout feature.

* vd/sparse-clean-etc:
  update-index: reduce scope of index expansion in do_reupdate
  update-index: integrate with sparse index
  update-index: add tests for sparse-checkout compatibility
  checkout-index: integrate with sparse index
  checkout-index: add --ignore-skip-worktree-bits option
  checkout-index: expand sparse checkout compatibility tests
  clean: integrate with sparse index
  reset: reorder wildcard pathspec conditions
  reset: fix validation in sparse index test

diff --cc builtin/clean.c
Simple merge

diff --cc builtin/reset.c
Simple merge

diff --cc builtin/update-index.c
Simple merge

diff --cc read-cache.c
Simple merge

diff --cc t/t1092-sparse-checkout-compatibility.sh
Simple merge