Changes to support Intel AVX/AVX2 in cvResize().

This patch
- adds code path for Intel AVX2 detection, and
- utilizes Intel AVX/AVX2 intrinsics within cvResize()

check_regression=*esize*
hm, according to this: http://www.virtualdub.org/blog/pivot/entry.php?id=347, if I put /arch:AVX or /arch:AVX2, the code will likely crash on CPUs without AVX/AVX2 support. I see that this is not you who introduced the problem, we also have the same problem with SSE 4.x. But since OpenCV checks in runtime whether architecture supports SSE4.x/AVX/AVX2, can we somehow enable your fast branches of resize (and maybe other functions) and at the same time keep the backward compatibility with older CPUs?