Use ff_url_join for assembling URLs, instead of snprintf
This ensures proper escaping of numerical IPv6 addresses.
The RTSP (de)muxer needs its own network initialization, since it isn'ta protocol and url_open hasn't been called yet.
Originally committed as revision 22226 to svn://svn.ffmpeg.org/ffmpeg/trunk
Gopher protocol, patch by Toshimitsu Kimura, lovesyao gmail com
Originally committed as revision 17159 to svn://svn.ffmpeg.org/ffmpeg/trunk