Circumventing cblas_sgemv segfault in Accelerate

http://article.gmane.org/gmane.comp.python.scientific.devel/19141
https://github.com/numpy/numpy/issues/4007

Ok, I will use this:

```C
#define cpu_supports_avx()\
(system("sysctl -n machdep.cpu.features | grep -q AVX") == 0)

#define using_mavericks()\
(system("sw_vers -productVersion | grep -q 10\\.9\\.") == 0)
```