cmake: detect clang compiler anf fix some link issues
ipfilter: remove two unused functions
ipfilter: remove two unreferenced functions
intra: remove an unreferenced function
pixel: remove vector class headers from pixel-ssse3.cpp
vector: bypass a number of functions we do not use when compiled by clang

The sooner these classes go away the better
blockcopy: isolate vector class routines together (firing squad)
cmake: enable clang to compile intrinsic primitives without version checks
api: add API version to x265_encoder_open to prevent dynamic library link skew

Gratefully borrowed from x264

--HG--
extra : amend_source : a4233ad7d69fc7dcb22d2ef6f4b7a0bcf4d7d6eb
encoder: silence idiotic compiler warning from VC10
api: make notice of how the build number now must be echoed in x265.def
TEncSeach: add alignment to bidir output buffer

fixes crash in x265_pixel_avg_w16_sse2 from aligned writes to the output buffer