As part of merging subtitle-in-terminal changes make
update_subtitles() only clear existing subtitles if called with the
reset argument, and not try to set new ones. Later calls should set
the needed new subtitles, and this change avoids some problems with
trying to set subtitles when mp_property_sub() in command.c gets
called from initialization code before full initialization.
Lack of -fixed-vo causes the output window to be recreated not only
when changing files but also when switching the video stream, and that
happens when moving from one ordered chapter source to another. Having
the window disappear and reappear (likely at another location if it
was ever moved) is just too annoying.
Name the field "sub_id" as it's not specific to DVD subs.
Remove some other unused extern declarations together with dvdsub_id
from demux_mkv.c and demux_lavf.c.
First part of option restructuring. The aim is to move option values
from a huge number of separate globals to a single non-global struct.
This part adds some support for parsing option values into such struct
instances, and moves one example option (fixed-vo) to the struct.
