promisor-remote: compare remote names case sensitively

promisor-remote: compare remote names case sensitively

Because the "[remote "nick"] fetch = ..." configuration variables
have the nickname in the second part, the nicknames are case
sensitive, unlike the first and the third component (i.e.
"remote.origin.fetch" and "Remote.origin.FETCH" are the same thing,
but "remote.Origin.fetch" and "remote.origin.fetch" are different).

Let's follow the way Git works in general and compare the remote
names case sensitively when processing advertised remotes.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>