cleanup and fixes.

If too much frames have been dropped, then only decode I frames for a while and see if you can catch up with decoding other frames as well.

trustworthy here). 

Most noticeably, this adds support for RTSP, SDP-to-disk and SDP-over-HTTP
to RTP/TS. In particular, --sout '#rtp{mux=ts}' now works even without a
fixed destination

compiler warnings (such as buffer overflows detected at compile time!)

Please fix it *** IF YOU KNOW WHAT YOU ARE DOING ***

Uses --no-media-library if you don't want to use it (see #1047)

Remembers art url when an input with same artist & album needs art, so if it's a local file, it doesn't need to be copied in the cache.