http-push: when making directories, have a trailing slash in the path name

http-push: when making directories, have a trailing slash in the path name

The function lock_remote() sends MKCOL requests to make leading
directories; However, if it does not put a forward slash '/' at the end of
the path, the server sends a 301 redirect.

By leaving the '/' in place, we can avoid this additional step.

Incidentally, at least one version of Curl (7.16.3) does not resend
credentials when it follows a 301 redirect, so this commit also fixes
a bug.

Original patch by Tay Ray Chuan <rctay89@gmail.com>.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>