options: change handling of "no-" options yet again

Commit 4a40eed "options: change handling of "no-" options" generally
improved the handling of automatically added negation options
(recognizing "--no-opt", even though only "--opt" is declared in the
option list).

Unfortunately, one corner case was missed, which broke the option
"--input=no-default-bindings" (other suboptions, e.g. VO suboptions,
were not affected, and this is the only option where this mattered).

Instead of increasing the complexity further, use a completely different
approach: add the "--no-" options at runtime, and make them behave like
real options. This approach could be considered slightly less elegant,
because the code now has to worry about some option implementation
details rather than leaving it to the parser, but all in all the new
code is simpler and there are less weird corner cases to worry about.
osd: always update already visible OSD bar on seeks

Seeks can be performed with OSD bar invisible (e.g. "osd-msg seek ..."
command), and then an already visible bar won't be updated. But the bar
will stick around until the OSD text is hidden. This is confusing, so
change it that the bar is updated. (Making the bar disappear on such
seeks would require much more changes, so we're lazy and go with this
commit.)
osd: add --no-osd-bar option to disable the OSD bar

In addition to disabling the OSD bar physically, also add some fallbacks
to OSD text in places the OSD bar would have been used.
command: give feedback on the OSD if a property is unavailable

Until now, setting a property that is not available (e.g. deinterlacing
if not using vdpau and no deinterlacing filter is inserted) silently
failed (except for a messager on the terminal). Instead show on the OSD
that the property is unavailable.
mplayer: use talloc instead of malloc for status line
osd: add --osd-status-msg option for custom OSD status
cleanup: remove duplicated function, move escape parsing function
demux_mf: fix breakage after commit 4d016a9
command: add "cache" read-only property
osd: show cache state on the playback progression display by default

This affects the "show_progress" command, by defualt on the 'P' key.

If there are complaints, I'll probably remove it again. (It looks
relatively annoying, but it also valueable information... sort of.)
mplayer: print "Cache:" instead of "C:" on the status line

Hasn't been done before because there wasn't enough space, but this
changed recently.
manpage: improve configuration file section a bit
osd: use --osd-duration for OSD bar

It was hardcoded to 1 second (which is also the default for
--osd-duration, so this was probably never noticed).
parser-cfg: fix profile-desc

Printed "error parsing option profile-desc=..." when using that inside
of profile sections. This happened because we now check the presence of
an option before setting it, and profile-desc is not an option, but
special cased in the config parser.
demux_lavf: add workaround for broken libavformat seek behavior

Seeking before the start of a .flac file (such as seeking backwards when
the file just started) generates a bunch of decoding errors and audible
artifacts. Also, the audio output doesn't match the reported playback
position. The errors printed to the terminal are:

[flac @ 0x8aca1c0]invalid sync code
[flac @ 0x8aca1c0]invalid frame header
[flac @ 0x8aca1c0]decode_frame() failed

This is most likely a problem with the libavformat API. When seeking
with av_seek_frame() fails, the demuxer can be left in an inconsistent
state. ffplay has the same issue [1].

Older versions of mpv somehow handled this fine. Bisection shows that
commit b3fb7c2 caused this regression by removing code that retried
failed seeks with an inverted AVSEEK_FLAG_BACKWARD flag. This code was
removed because it made it harder to stop playback of a file by seeking
past the end of the file (expecting this is rather natural when skipping
through multiple files by seeking, and the internal mplayer demuxers
also did this).

As a workaround, re-add the original code, but only for the backwards
seeking case.

Also note that the original intention of the code removed in b3fb7c2 was
not dealing with this case, but something else. It also had to do with
working around weird libavformat situations, though. It's not perfectly
clear what exactly. See commit 1ad332f.

[1] https://ffmpeg.org/trac/ffmpeg/ticket/2282