avio: add avio_open2, taking an interrupt callback and options

avio: add avio_open2, taking an interrupt callback and options

The interrupt callback has to be passed in during opening (setting it
after opening isn't enough), since a blocking open couldn't be
interrupted otherwise.

Options are passed down to procotols and also need to be available
during open() in most cases.

Signed-off-by: Anton Khirnov <anton@khirnov.net>