avio access: use new API

- fix bug in ACCESS_GET_PTS_DELAY where it would fall through the next case
- print error messages from libavformat
- remove useless strdup
- check for exclusive access to avio when context open succeeded
- support for multiple input / output at the same time with libavformat > 54 (untested)
(cherry picked from commit cca698a0)
Signed-off-by: KO Myung-Hun <komh@chollian.net>
Signed-off-by: Rafaël Carré <funman@videolan.org>