Merge branch 'ss/safe-create-leading-dir-with-slash'

"git clone $origin foo\bar\baz" on Windows failed to create the
leading directories (i.e. a moral-equivalent of "mkdir -p").

* ss/safe-create-leading-dir-with-slash:
safe_create_leading_directories(): on Windows, \ can separate path components

diff --cc sha1_file.c
Simple merge