We make several starts_with() calls, only to advance
pointers. This is exactly what skip_prefix() is for, which
lets us avoid manually-counted magic numbers.
Helped-by: Pranit Bauva <pranit.bauva@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>