input: silence warning if input.conf is missing

It's silly to print a warning if an optional config file is missing.
Don't print anything at the default message level if an input config
is not found.

Unfortunately, the behavior is the same for explicitly passed input
config files (with --input=conf=file.conf).
manpage: various fixes
configure: remove --enable-profile

The --enable-profile switch simply adds -p to the CFLAGS, which enables
gcc's extremely worthless "prof" profiling support. This kind of
profiling is broken on the conceptual level and thus harmful, and even
if you want it, you can enable it manually with --extra-cflags.

Also remove $_march $_mcpu from the CFLAGS code. These variables were
always unset, as the code setting them has been removed earlier.
options, vo_x11: remove -zoom option, make it default

The -zoom option enabled scaling with vo_x11. Remove the -zoom option,
and make its behavior default. Since vo_x11 has to use libswscale for
colorspace conversion anyway, which doesn't do actual extra scaling when
vo_x11 is run in windowed mode, there should be no speed difference with
this change.

The code removed from vf_scale attempted to scale the video to d_width/
d_height, which matters for anamorphic video and the --xy option only.
vo_x11 can handle these natively. The only case for which the removed
vf_scale code could matter is encoding with vo_lavc, but since that
didn't set VOFLAG_SWSCALE, nothing actually changes.
vo_opengl: remove osdcolor suboption

This wasn't actually used since the old gray-alpha OSD rendering has
been removed. Removing the documentation for the vo_opengl_old osdcolor
suboption was forgotten as well.
video/filter: rename vf_eq2 to vf_eq

vf_eq was deleted earlier, which makes the name vf_eq2 even more
awkward.
options: remove --osdlevel in favor of --osd-level

--osdlevel has been documented as renamed/removed. Not actually
removing it was probably an oversight.
options: rename --xineramascreen to --screen, remove magic values

--xineramascreen=-2 becomes --screen=all
--xineramascreen=-1 becomes --screen=current
options: remove --display

Was used to set the X11 display. XDisplayName(NULL) does the same,
using the DISPLAY environment variable instead.
options: respect --no-msgcolor during early program start

Using --no-msgcolor, error messages that happened before "really"
parsing the command line were still printed in color. Add the
CONF_PRE_PARSE flag to make this option take effect as early as
possible.
cookies: don't read cookie files from ancient browsers

Remove the code that attempted to read cookie files from well-known
browser locations. This code was written for ancient browsers, and only
knew about Mozilla and Netscape. While it's possible that these browsers
are still alive and still use the same config locations and cookie file
formats, the only Mozilla-based browser that still matters is Firefox.
Firefox uses a sqlite database for cookies, located in a slightly
different config path.

Just remove this code.
options: rename -ss and -endpos, allow relative times

Rename the -ss option to -start, and -endpos to -length. Add a -end
option. The -end option always specifies an absolute end time, as
opposed to -endpos/-length.

All these options (--start, --end, --length) now accept relative times.
Percent positions (e.g. "--start=30%") are interpreted as fractions of
the file duration. Negative times (e.g. "--start=-1:00) are interpreted
relative to the end of the file. Chapters (e.g. "--start=#3") yield the
chapter's time position.

The chapter support might be able to replace --chapter completely, but
for now I am not sure how well this works out with e.g. DVDs and BDs,
and a separate --chapter option is useful interface-wise.
options: --field-dominance: replace magic number values with choices

--field-dominance=-1  becomes --field-dominance=auto
--field-dominance=0   becomes --field-dominance=top
--field-dominance=1   becomes --field-dominance=bottom
options: rename --cursor-autohide, replace magic number values

--cursor-autohide-delay=-2   becomes --cursor-autohide=always
--cursor-autohide-delay=-1   becomes --cursor-autohide=no
--cursor-autohide-delay=123  becomes --cursor-autohide=123
options: rename -sub-fuzziness to -autosub-match, change option values

"--autosub-match" is close to "--autosub", and reflects what this
option does slightly better. Replace the magic number option values
with choices:

--sub-fuzziness=0  becomes --autosub-match=exact
--sub-fuzziness=1  becomes --autosub-match=fuzzy
--sub-fuzziness=2  becomes --autosub-match=all
options: add --mute for setting initial audio mute status

Similar to --volume. Takes this as opportunity to move the variable
corresponding to --volume into MPOpts.
subreader: replace sub_free() by talloc destructor

Makes it less annoying to free the sub_data.
command: add sub_reload and sub_remove commands

sub_remove remove an external subtitle track, for whatever this may be
needed.

sub_reload removes and re-adds an external subtitle track.

Also rename sub_load to sub_add, because that seems to be more in line
with sub_remove.
core: add --keep-open, which doesn't close the file on EOF

The --keep-open option causes mpv not to close the current file.
Instead, it will pause, and allow the user to seek around. When
seeking beyond the end of the file, mpv does a precise seek back to
the previous last known position that produced video output.

In some corner cases, mpv might not be able to produce video output at
all, despite having created a VO. (Possibly when only 1 frame could be
decoded, but the video filter chain queues frames. Then a VO would be
created, without sending an actual video frame to the VO.) In these
cases, the VO window will not redraw, not even OSD.

Based on a patch by coax [1].

[1] http://devel.mplayer2.org/ticket/210#comment:4
mplayer: refactor: move computation of a/v sync

The computation for the A/V sync value was inside print_status(). Move
it into its own function; this makes things simpler and gets rid of some
minor dead code.