Merge branch 'kf/http-proxy-auth-methods'

New http.proxyAuthMethod configuration variable can be used to
specify what authentication method to use, as a way to work around
proxies that do not give error response expected by libcurl when
CURLAUTH_ANY is used.  Also, the codepath for proxy authentication
has been taught to use credential API to store the authentication
material in user's keyrings.

* kf/http-proxy-auth-methods:
  http: use credential API to handle proxy authentication
  http: allow selection of proxy authentication method

diff --cc Documentation/config.txt
Simple merge

diff --cc remote.c
Simple merge