This commit removes the "old" networking code in favor of libavformat's
code.
The code was still used for mp_http, udp, ftp, cddb. http has been
mapped to libavformat's http support since approximately 6 months ago.
udp and ftp have support in ffmpeg (though ftp was added only last
month). cddb support is removed with this commit - it's probably not
important and rarely used if at all, so we don't care about it.
The "http:" protocol has been switched to use ffmpeg's HTTP
implementation some time ago. One problem with this was that many HTTP
specific options stopped working, because they were obviously
implemented for the internal HTTP implementation only.
Add the missing things. Note that many options will work for ffmpeg
only, as Libav's HTTP implementation is missing these. They will
silently be ignored on Libav.
Some options we can't fix:
--ipv4-only-proxy, --prefer-ipv4, --prefer-ipv6
As far as I can see, not even libavformat internals distinguish
between ipv4 and ipv6.
--user, --passwd
ffmpeg probably supports specifying these in the URL directly.
