http: Turn on verbose Curl messages if GIT_CURL_VERBOSE set in environment

Signed-off-by: Mark Wooding <mdw@distorted.org.uk>
Signed-off-by: Junio C Hamano <junkio@cox.net>

http.c

@@ -192,6 +192,9 @@ static CURL* get_curl_handle(void)
 
 	curl_easy_setopt(result, CURLOPT_FOLLOWLOCATION, 1);
 
+	if (getenv("GIT_CURL_VERBOSE"))
+		curl_easy_setopt(result, CURLOPT_VERBOSE, 1);
+
 	return result;
 }