Merge branch 'ep/http-curl-trace'

HTTP transport gained an option to produce more detailed debugging
trace.

* ep/http-curl-trace:
  imap-send.c: introduce the GIT_TRACE_CURL enviroment variable
  http.c: implement the GIT_TRACE_CURL environment variable

imap-send.c

@@ -1443,6 +1443,7 @@ static CURL *setup_curl(struct imap_server_conf *srvc)
 
 	if (0 < verbosity || getenv("GIT_CURL_VERBOSE"))
 		curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
+	setup_curl_trace(curl);
 
 	return curl;
 }