Merge branch 'jt/sparse-checkout-leading-dir-fix'

"git sparse-checkout init" failed to write into $GIT_DIR/info
directory when the repository was created without one, which has
been corrected to auto-create it.

* jt/sparse-checkout-leading-dir-fix:
  sparse-checkout: create leading directory

diff --cc builtin/sparse-checkout.c
Simple merge

diff --cc t/t1091-sparse-checkout-builtin.sh
Simple merge