private static String formatTimeSpan(final long before) {
            // don't use String.format in a pure logging routine, it has very bad performance
            return " (" + (System.currentTimeMillis() - before) + " ms) ";
        }
Add headers to HTTP request.

@param request   the request builder to add headers to
@param headers   the headers to add (in addition to the standard headers), can be null
@param cacheFile if non-null, the file to take ETag and If-Modified-Since information from
main/src/main/java/cgeo/geocaching/network/Network.java