Continued improvement of AVX support (vec<float,8> and vec<double,4> sin & cos support), tested on OS X

currently sin< vec<float,8> > and cos< vec<float,8> > are MUCH slower than the vec<double,4> variants, around 16x according to the sse_mathfun_test.c benchmark … and this appears to be due to the use of _mm256_castsi256_ps ?!