ass_parse: remove 2 unused variables

Fallout from the previous commits.
configure.ac: Treat DragonFly as the rest of BSDs
Fix integer overflow in FT_Outline
Merge pull request #116 from hadvaid/dragonfly

configure.ac: Treat DragonFly as the rest of BSDs
Merge pull request #119 from MrSmile/fix-drawing-overflow

Fix integer overflow in FT_Outline
Fix \fade(7-argument version) parse
Try to speed up event lookup

Try to avoid cases where libass will unnecessarily iterate over the
whole event list during playback.

1. Potentially speed up check_duplicate_event() by storing all found
ReadOrder IDs in a sorted array. Now only a binary search is needed to
check whether a Matroska-demuxed event was already added. (Probably
could be simplified by using a bitmap instead - but ReadOrder could be
arbitrarily high in malicious files.)

2. Sort event array by start time, and optimize for the case when
ass_render_frame() is called with monotonically increasing video
timestamps. We can start with the first known-to-be-rendered event, and
stop with the first event that has a too high start time.

Since this needs sorting on the event array, this can't be done without
some cooperation by the libass API user. See ass_set_fast_event_lookup()
doxygen comment for details.
Try using a bitmap instead of an array

Somehow this didn't reduce the amount of code...

It might be faster and more memory efficient, at least if the source
file is well-behaved, and ReadOrder numbers are consecutive.