added objects for 'force bold' and 'opacity'

Also implement correct run-time POSIX clock selection.

thanks for the explanation to courmisch

as we'll need seekpoints for UI: chapters offsets were not sufficient.

This lifts the PATH_MAX characters limit, and should fix encoding on
POSIX non-UTF-8 systems.

Decoders are never "killed", so this had no effects.

(Same reasons as VLC_OBJECT_AOUT)

Audio output is not a descendent of input thread, so there was no real
use for this object type anymore.