Update ffmpeg and switch to w32threads
Add helper functions for safe unicode transformations.
Check all uses of MultiByteToWideChar and WideCharToMultiByte

Fixes issue 452.
Update libbluray
Update ffmpeg
Disable native opus decoder until the swresample/avresample situation is worked out.

Opus decoding is still supported through libopus, of course.
Fix safe conversions functions in the case of too long inputs
Switch optimized converter functions back to custom SSE2 memory copy.
Optimize and simplify SSE2 load/store
Move plane_copy to pixconv.cpp
Implement plane_copy_sse2, optimized plain copying of frames.
Update plane_copy to be the same as plane_copy_sse2 without the SSE2 copy.
biPlanes is documented to always be 1.
Remove unused function
Fix yuv422 -> yuyv/uyvy crash
Convert dstStride to ptrdiff_t
Convert frame stride to ptrdiff_t
[MPC-HC] Use our own ffmpeg clone repository.

WARNING: This should be the first custom commit in our fork and its title should not be modified.
[MPC-HC] LAV Splitter: Exhibits MKV attachments through IDSMResourceBag interface.
[MPC-HC] Tray icon: Add an optional custom callback for "show property page" events.