Allow HTTP proxy to be overridden in config

The http_proxy / HTTPS_PROXY variables used by curl to control
proxying may not be suitable for git.  Allow the user to override them
in the configuration file.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -550,6 +550,10 @@ specified as 'gitcvs.<access_method>.<varname>' (where 'access_method'
 is one of "ext" and "pserver") to make them apply only for the given
 access method.
 
+http.proxy::
+	Override the HTTP proxy, normally configured using the 'http_proxy'
+	environment variable (see gitlink:curl[1]).
+
 http.sslVerify::
 	Whether to verify the SSL certificate when fetching or pushing
 	over HTTPS. Can be overridden by the 'GIT_SSL_NO_VERIFY' environment

http.c

@@ -24,6 +24,7 @@ char *ssl_cainfo = NULL;
 long curl_low_speed_limit = -1;
 long curl_low_speed_time = -1;
 int curl_ftp_no_epsv = 0;
+char *curl_http_proxy = NULL;
 
 struct curl_slist *pragma_header;
 
@@ -160,6 +161,13 @@ static int http_options(const char *var, const char *value)
 		curl_ftp_no_epsv = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp("http.proxy", var)) {
+		if (curl_http_proxy == NULL) {
+			curl_http_proxy = xmalloc(strlen(value)+1);
+			strcpy(curl_http_proxy, value);
+		}
+		return 0;
+	}
 
 	/* Fall back on the default ones */
 	return git_default_config(var, value);
@@ -205,6 +213,9 @@ static CURL* get_curl_handle(void)
 	if (curl_ftp_no_epsv)
 		curl_easy_setopt(result, CURLOPT_FTP_USE_EPSV, 0);
 
+	if (curl_http_proxy)
+		curl_easy_setopt(result, CURLOPT_PROXY, curl_http_proxy);
+
 	return result;
 }