Blender Git Loki

Decklink: fix output on some DeckLink cards.

Opening a DeckLink card for output with the DeckLink object
sometimes failed because some types of card report no support for BGRA pixel
format, yet it works. The test is maintained but a warning is printed
instead of throwing an exception.

Optional cache size suffix added in Decklink output format string: may be
needed for some card that needs more than the default 8 frames.