[x265] refine deblocking filter

[Steve Borho]

On 09/25, Satoshi Nakagawa wrote:
> I can't reproduce it.
> 
> 940cec3bf0b4 and 532d0266e333 (parent) are same results.
> no mismatch.

Whatever the problem is, it must be subtle. I couldn't reproduce the
problem myself (still can't) but on our test systems and on Deepthi's
system it is very reproducible and obvious.

 before 940cec3bf0b4
 encoded 30 frames in 1.75s (17.10 fps), 4170.76 kb/s

 after 940cec3bf0b4
 encoded 30 frames in 4.07s (7.38 fps), 10811.39 kb/s

It might require VC11 x86_64, not sure. I ran an encode through
valgrind on Mac and it did not find anything.

-- 
Steve Borho