Win32: add support for play and pause buttons in media keys (different from a plya/pause unique button

Tested with an Apple remote v1, and a HP media center remote. I don't know how to get the "menu" message" from the remote.

Apparently libvlc_time_t is millisec, whereas mtime_t is microsecs.
Most event callbacks where carying an incorrect mtime_t value.

We could handle directories as descriptors, but we currently don't. In
the mean time, we had better show an error than generate corrupt
playlist entries.

"-" is now converted to "fd://0" by the input code. And file:///- really
means /- (which is a valid file name).

venc=x264{slices,slice-max-size,slice-max-mbs} options are there now

libx264 gives dts-value, but we need to calculate initial delay, so dts doesn't
go < VLC_TS_0.

Tell how many frames are still left on libx264 buffer when we close encoder

Only set BLOCK_FLAG_TYPE_I on IDR-frames on X264_BUILD < 83 and only those
which have b_keyframe on X264_BUILD >= 83.

We assume it is present in plenty of places anyway

This requires support for fdopendir(). One open() and fstat() calls per
input file are avoided. Ok, this is not such a major improvement).
This should also work around brain-damaged file system drivers such as
Linux HFS+, whereby opendir() succeeds on regular files.

directory does not register the "fd" shortcut, so the standard input
case should not occur.

(You can't read ahead a pipe)

InputSourceInit() does it globally already