This mitigates persistent overruns in some scenarios.

TODO: replace nonblocking behavior with a blocking one

TODO: fix and reenable

+ some rewrite allowing more than 2 buffers (currently only macro)

First frame has index 00000001.<ext>, the same as mplayer so that frames
produced by mplayer can be directly played with UltraGrid.

Print messages of what was entered incorrectly in the configuration
string.

Fixed detection of JPEG and SAGE libraries Fixed message output after compilation & bug in installing license file

TODO: Think the whole stuff over - do we prefer finishing explicitly
grab function if there are no frames? Or rather we want "non-blocking"
(eg. timedwait) calls in _grab functions? The first one is somehow
cleaner but also harder to implement. Anyway, currently is finish called
just before done function, so its currently not serving it purpose.

* display more user-friendly message instructing to report bugs

Do not try to wait for buffer swap with every packet.