Merge branch 'jk/sparse-fdleak-fix'

A file descriptor left open is now properly closed when "git
sparse-checkout" updates the sparse patterns.

* jk/sparse-fdleak-fix:
  sparse-checkout: use fdopen_lock_file() instead of xfdopen()
  sparse-checkout: check commit_lock_file when writing patterns
  sparse-checkout: consolidate cleanup when writing patterns