Merge branch 'ds/commit-and-checkout-with-sparse-index'

Merge branch 'ds/commit-and-checkout-with-sparse-index'

"git checkout" and "git commit" learn to work without unnecessarily
expanding sparse indexes.

* ds/commit-and-checkout-with-sparse-index:
  unpack-trees: resolve sparse-directory/file conflicts
  t1092: document bad 'git checkout' behavior
  checkout: stop expanding sparse indexes
  sparse-index: recompute cache-tree
  commit: integrate with sparse-index
  p2000: compress repo names
  p2000: add 'git checkout -' test and decrease depth