Make some syntax change to follow coding style.

Update the proxy detection for a remote.

1. Honor `http.<url>.proxy` syntax for a remote's direct URL and
   parent URLs.
2. Honor an empty configuration URL to override a proxy configuration.

Add tests to ensure that configuration specificity is honored.

Item 2 of 3 from #4164

Signed-off-by: Mathieu Parent <math.parent@gmail.com>

Set Host Header to match CONNECT authority target

Prior to this change, for CONNECT requests, the Host header was set to
the host and port of the target http proxy. However, per the rfc7230 for
HTTP/1.1 this is incorrect as the Host header should match the target of
the CONNECT request, as detailed in section 5.3.3 & 5.4.

  5.3.3.  authority-form

   The authority-form of request-target is only used for CONNECT
   requests (Section 4.3.6 of [RFC7231]).

     authority-form = authority

   When making a CONNECT request to establish a tunnel through one or
   more proxies, a client MUST send only the target URI's authority
   component (excluding any userinfo and its "@" delimiter) as the
   request-target.  For example,

     CONNECT www.example.com:80 HTTP/1.1

  5.4.  Host

   <snip>

   A client MUST send a Host header field in all HTTP/1.1 request
   messages.  If the target URI includes an authority component, then a
   client MUST send a field-value for Host that is identical to that
   authority component, excluding any userinfo subcomponent and its "@"
   delimiter (Section 2.7.1).  If the authority component is missing or
   undefined for the target URI, then a client MUST send a Host header
   field with an empty field-value.

This issue was noticed when proxying requests through HAProxy 2.2 which
rejects these invalid http requests.

The ntlmclient dependency can now dynamically load OpenSSL.

Attempt authentication when a username is presented but a password is
not; this can happen in particular when users are doing token
authentication and specifying the token in the URL itself.  For example,
`https://token@host/` is a valid URI and should be treated as a username
of `token` with an empty password.

Makes usage of CLOCK_MONOTONIC conditional and makes functions that uses
git__timer handle clock resynchronization.

Call gettimeofday with tzp set to NULL as required by
https://pubs.opengroup.org/onlinepubs/9699919799/functions/gettimeofday.html