v2, 3 partshttp: proxy support improvements

So here is v2 of proxy authentication support patch-set, the following modifications were done as per discussion:

- PATCH 1/1: Extended commit message

- PATCH 2/2: Extended commit message and only read http_proxy
(discard HTTP_PROXY).

- PATCH 3/3: Extended commit message and use credential api for
retrieving password from user, taking care we only ask it once
for multiple curl handles case.

Nelson Benitez Leon (3):
  http: authenticate on NTLM proxies and others suppported by CuRL
  http: try http_proxy env var when http.proxy config option is not set
  http: when proxy url has username but no password, ask for password

 http.c |   27 +++++++++++++++++++++++++--
 1 files changed, 25 insertions(+), 2 deletions(-)