avcodec: allocate one additional hardware surface for MPEG-2

Required to avoid visual glitches when running out of free surfaces
with avcodec and vaapi/dxva2 backends.

Fix #10868
macosx dialog provider: fix misleading (and duplicate) module shortcut
macosx dialog provider: fix compilation warnings
httplive: have some sane max_duration_length

Regression from ac3f61953b25a61cf46c16badcfd2a24f890b83e as without this
there could be negative/zero max_duration_length if playlist didn't
change and it would cause instantenious refetch of that playlist.
httplive: use CLOCK_FREQ
macosx dialog provider: relicense to LGPLv2.1+ for use within VLCKit

Agreed by Pierre d'Herbemont, Sebastian Zwickert, Rémi Denis-Courmont, Jean-Baptiste Kempf and me
build system: add conditional variables to differenciate between iOS and OS X

This allows automagic enabling and disabling of the needed and useful aout and vout modules
configure: fix compilation on non-Darwin platforms
extras/ios: remove dropped configure options from build script and disable audioqueue aout
extras/macosx: remove dropped options from configure script
transcode: add more channels on audio

Assume that 3 channels is 2.1 instead of 3 front channels,
also 6 is 5.1.

Ref #1897
avcodec:multichannel encoding support

Make some assumptions on channels, like 6 channels is 5.1 etc.

Ref #1897
audioqueue: fix compilation when enabled with --enable-audioqueue
Add basic iOS dialog provider

There is no support for progress dialogs so far
Update NEWS and module list
Freetype: allow to pass a font on WinRT
Freetype: do not ship dead code on WinRT dll

This allows freetype.dll to pass WACK
gl: make/release current context as appropriate
xcb/glx: make context current as appropriate
aout: add rounding to playlist_VolumeUp

Additional rounding step ensures that new volume is a multiple of the
"volume-step" as defined in libvlc-module.c.

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>