The function has to do three small and independent tasks, but all of them
were crammed into a single loop. This rewrites the function entirely by
unrolling these tasks.
We also now use is_dir_sep(c) instead of c == '/' to increase portability.
Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at> Signed-off-by: Junio C Hamano <gitster@pobox.com>