http.c: don't assume that urls don't end with slash

http.c: don't assume that urls don't end with slash

Make append_remote_object_url() (and by implication,
get_remote_object_url) use end_url_with_slash() to ensure that the url
ends with a slash.

Previously, they assumed that the url did not end with a slash and
as a result appended a slash, sometimes errorneously.

This fixes an issue introduced in 5424bc5 ("http*: add helper methods
for fetching objects (loose)"), where the append_remote_object_url()
implementation in http-push.c, which assumed that urls end with a
slash, was replaced by another one in http.c, which assumed urls did
not end with a slash.

The above issue was raised by Thomas Schlichter:

  http://marc.info/?l=git&m=125043105231327

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Tested-by: Thomas Schlichter <thomas.schlichter@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>