Optimize BackwardReferenceHashChainFollowPath.

Instead of calling HashChainFindMethod, call a new (subset) method
HashChainFindOffset to get the offset/distance for a given length.

The encoding is tad faster at default compression

                       Before              After
                     bpp/rate            bpp/rate
442 Palette     0.2720/5.270 MP/s      0.2720/5.790 MP/s
558 non-palette 3.7607/0.797 MP/s      3.7607/0.816 MP/s

Change-Id: If4041a9c18f7e972f49fcbab8c3e2f013d8bf1cf
stopwatch.h: fix includes

WEBP_INLINE -> webp/types.h
memcpy -> string.h

Change-Id: Iab2ea8b553dc98be75eede751de62ab0292d1f97
PrintReg: output to stderr

allows use of '-o -' while testing

Change-Id: Ibc02d7cede2df4eb8be0a28c0ca4bf5e91864191
Merge "stopwatch.h: fix includes"
Merge "PrintReg: output to stderr"
make VP8PredLuma4[] non-const and initialize array in VP8DspInit()

also convert 'type *dst' to 'type* dst'

Change-Id: I41ab66ad15b548cc45d1cb8b10bbca4fe1528cae
implement VE4/HE4/RD4/... in SSE2

(30% faster prediction functions, but overall speed-up is ~1% only)

Change-Id: I2c6e7074aa26a2359c9198a9015e5cbe143c2765