swipe pattern StopIteration fixes

Signed-off-by: Paul Brook <paul@nowt.org>
Fix double buffering issues

Signed-off-by: Paul Brook <paul@nowt.org>

Conflicts:
	patterns/cubefill.py
	patterns/worm.py
Tweak worm pattern timing code.

Signed-off-by: Paul Brook <paul@nowt.org>
Tweak boxflip pattern timing code.

Signed-off-by: Paul Brook <paul@nowt.org>
Tweal fireworks pattern StopIteration logic

Signed-off-by: Paul Brook <paul@nowt.org>