TComPicYuv: remove unused include
TComPicYuv: fix padding of picture buffers

Ensure row starts are at a multiple of 32, this causes strides to be multiple
of 64.  Before this patch, strides we capable of being multiples of 8, causing
alignment exceptions for some videos.
weightp: use source reference frames for weight analysis

This fixes weightp when used in combination with frame parallelism, where the
reference's reconstructed picture is most likely not yet avaialable.

Some measurements using the sintel 480p clip
no-weightp -F1: 408.47s (3.07 fps), 144.63 kb/s, Global PSNR: 48.956
no-weightp -F3: 361.14s (3.47 fps), 144.01 kb/s, Global PSNR: 48.746

Prior to this change (recon refs used for weightp analysis):
weightp -F1: 402.84s (3.11 fps), 131.09 kb/s, Global PSNR: 49.908
x265 [info]: 278 of 687 (40.47%) P frames weighted
weightp -F3: 355.88s (3.52 fps), 132.09 kb/s, Global PSNR: 49.768
x265 [info]: 242 of 687 (35.23%) P frames weighted

After this change (source refs used for weightp analysis):
weightp -F1: 404.83s (3.10 fps), 131.82 kb/s, Global PSNR: 49.414
x265 [info]: 325 of 687 (47.31%) P frames weighted
weightp -F3: 348.32s (3.60 fps), 131.01 kb/s, Global PSNR: 49.957
x265 [info]: 325 of 687 (47.31%) P frames weighted

Because of the lower bitrate, enabling weightp actually makes this clip encode
faster.  No idea why -F1 has so much less PSNR than -F3; needs investigation.
Merge with stable
reference: more robust initialization, remove m_startPad member variable

m_startPad was only used in the init() function so it could be an auto-var