http-fetch: redact url on die() message

http-fetch: redact url on die() message

http-fetch prints the URL after failing to fetch it. This can be
confusing to users (they cannot really do anything with it), and they
can share by accident a sensitive URL (e.g. with credentials) while
looking for help.

Redact the URL unless the GIT_TRACE_REDACT variable is set to false. This
mimics the redaction of other sensitive information in git, like the
Authorization header in HTTP.

Fix also capitalization of previous die() message (must start in
lowercase).

Signed-off-by: Ivan Frade <ifrade@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>