t5563: add tests for basic and anoymous HTTP access

t5563: add tests for basic and anoymous HTTP access

Add a test showing simple anoymous HTTP access to an unprotected
repository, that results in no credential helper invocations.
Also add a test demonstrating simple basic authentication with
simple credential helper support.

Leverage a no-parsed headers (NPH) CGI script so that we can directly
control the HTTP responses to simulate a multitude of good, bad and ugly
remote server implementations around auth.

Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>