Ignore XYSCSS in y4m if the newer standard C tag is present

Apparently y4mscaler will generate 4:2:0 files with XYSCSS set to 444
Faster hpel_filter
On ssse3, use pmaddubsw for h filter too (similar to v filter).
Change 32-bit v and c filters to write the result non-temporal.
Add commented-out defines to disable non-temporal operation.
Hardly any black magic here, but still a measurable win especially for ssse3.
Faster cabac_encode_decision_asm
Minimizes instruction count, which also means smaller code.
Various other slight changes to allow more instruction level parallelism.
Faster rounding of chroma DC coefficients
Mixed-refs support for B-frames
Small speed cost, usually a few percent at most. Generally has lowest cost in cases when it isn't very useful. Up to ~2% better compression overall on highly complex sources.

Also fix a few minor bugs in B-frame analysis and various bits of cleanup.
Timecode input/output
--tcfile-in allows a user to specify a timecode v1 or v2 file to override input timestamps.
Useful for dealing with VFR input, especially when FFMS/LAVF support isn't available.
--tcfile-out writes a timecode v2 file containing the timecodes of the output file.
New --timebase option allows a user to change the stream timebase.
Intended primarily for forcing timebase with timecode files if necessary.
When using --seek, note that x264 will seek in the timecode file as well.
Blu-ray support: NAL-HRD, VFR ratecontrol, filler, pulldown
x264 can now generate Blu-ray-compliant streams for authoring Blu-ray Discs!
Compliance tested using Sony BD-ROM Verifier 1.21.
Thanks to The Criterion Collection for sponsoring compliance testing!

An example command, using constant quality mode, for 1080p24 content:
x264 --crf 16 --preset veryslow --tune film --weightp 0 --bframes 3 --nal-hrd vbr --vbv-maxrate 40000 --vbv-bufsize 30000 --level 4.1 --keyint 24 --b-pyramid strict --slices 4 --aud --colorprim "bt709" --transfer "bt709" --colormatrix "bt709" --sar 1:1 <input> -o <output>

This command is much more complicated than usual due to the very complicated restrictions the Blu-ray spec has.
Most options after "tune" are required by the spec.
--weightp 0 is not, but there are known bugged Blu-ray player chipsets (Mediatek, notably) that will decode video with --weightp 1 or 2 incorrectly.
Furthermore, note the Blu-ray spec has very strict limitations on allowed resolution/fps combinations.
Examples include 1080p @ 24000/1001fps (NTSC FILM) and 720p @ 60000/1001fps.

Detailed features introduced in this patch:

Full NAL-HRD compliance, with both VBR (no filler) and CBR (filler) modes.
Can be enabled with --nal-hrd vbr/cbr.
libx264 now returns HRD timing information to the caller in the form of an x264_hrd_t.
x264cli doesn't currently use it, but this information is critical for compliant TS muxing.

Full VFR ratecontrol support: VBV, 1-pass ABR, and 2-pass modes.
This means that, even without knowing the average framerate, x264 can achieve a correct bitrate in target bitrate modes.
Note that this changes the statsfile format; first pass encodes make before this patch will have to be re-run.

Pulldown support: libx264 allows the calling application to specify a pulldown mode for each frame.
This is similar to the way that RFFs (Repeat Field Flags) work in MPEG-2.
Note that libx264 does not modify timestamps: it assumes the calling application has set timestamps correctly for pulldown!
x264cli contains an example implementation of caller-side pulldown code.

Pic_struct support: necessary for pulldown and allows interlaced signalling.
Also signal TFF vs BFF with delta_poc_bottom: should significantly improve interlaced compression.
--tff and --bff should be preferred to the old --interlaced in order to tell x264 what field order to use.

Huge thanks to Alex Giladi and Lamont Alston for their work on code that eventually became part of this patch.
"CRF-max" support with VBV
This is a rather curious feature that may have more use than is initially obvious.
In CRF mode with VBV enabled, CRF-max allows the user to specify a quality level which the encoder will never go below, even due to the effects of VBV.
This is not the same as qpmax, which is not aware of issues like scene complexity.
Setting this WILL cause VBV underflows in any situation where the encoder would have needed to exceed the relevant CRF to avoid underflow.

Why might one want to do this even if it would cause VBV underflows?
In the case of streaming, particularly ultra-low-latency streaming, it may be preferable to drop frames than to display frames that are of too low a quality.
Thus, in extremely complex scenes, rather than display completely awful video, the streaming server could simply drop to a lower framerate.
Scenecuts, which normally look terrible under situations like single-frame VBV, could be handled by just displaying them a bit later and dropping frames to compensate.
In other words, it's better to see the scenecut 150ms delayed than for it to look like a blocky mess for 150ms.

On the caller-side, this would be handled by detecting the output size of x264's frames and dropping future frames to compensate if necessary.

This can also be used in normal encoding simply to ensure that VBV does not hurt quality too much (at the cost of potentially causing underflows).
This can help quite a lot when using single-frame VBV and sliced threads, where VBV can often be somewhat unstable.
Fix two nondeterminisms
Move noise reduction data into thread-specific data.
Use correct reference list for L1 temporal predictors.
Use x264_log in more places instead of fprintf
Shrink some arrays in x264_t
Also remove an unnecessary assignment from cache_load.
Save a few bits in slice headers
Don't override the maximum ref index in the slice header if it's the same as the default.
Also update the naming of the relevant variables in the PPS.
Fix link errors with newest gpac cvs
gpac decided to randomly break API and require us to use their own custom malloc and free.
Fix slightly wrong mp4 duration.
Add support for spaces to iPhone GAS preprocessor script
Fix typo in configure
Reformat profile restrictions in --fullhelp.

Put "no interlaced", "no lossless" on their own line to avoid them
running into the default options list.
Much more accurate B-skip detection at 2 < subme < 7
Use the same method that x264 uses for P-skip detection.
This significantly improves quality (1-6%), but at a significant speed cost as well (5-20%).
It also may have a very positive visual effect in cases where the inaccurate skip detection resulted in slightly-off vectors in B-frames.
This could cause slight blurring or non-smooth motion in low-complexity frames at high quantizers.
Not all instances of this problem are solved: the only universal solution is non-locally-optimal mode decision, which x264 does not currently have.

subme >= 7 or <= 2 are unaffected.
Faster x264_macroblock_encode_pskip
GCC is apparently unable to optimize out the calculation of a variable when it isn't used.
Two compatibility fixes
Add IA64 support in configure.