Add flag to fix compilation with non-Apple gcc.

This allows one to use -cc=gcc-4.8 when building scipy. Tested on Mavericks.

Also bumps the version to 0.13.1.

Without this, you'd get an error like: 
/usr/local/Cellar/gcc48/4.8.2/lib/gcc/x86_64-apple-darwin13.0.2/4.8.2/include/emmintrin.h:1224:1: note: expected '__m128i' but argument is of type 'vUInt32'
 _mm_srl_epi64 (__m128i __A, __m128i __B)

I found the fix in this thread:
https://groups.google.com/forum/#!topic/r-sig-mac/9ZBRVM_vTW8