Fixing Visual Studio compilation (works with VS2013) - note that FMA3 tests fail for now

This is a first attempt at adding support for Visual Studio 2013 (which supports most C++11 features, except the particular one used for the tests here which is unrestricted unions).

I got the tests to pass but FMA3 doesn't seem to pass. Here are the results :

    Num results: 505374
    Testing: arch_null
    Testing: arch_sse2
    Testing: arch_sse2_sse3
    Testing: arch_sse2_sse3_ssse3
    Testing: arch_sse2_sse3_ssse3_sse4p1
    Testing: arch_sse2_sse3_ssse3_sse4p1_avx
    Testing: arch_sse2_sse3_ssse3_sse4p1_avx_avx2
    Testing: arch_sse2_sse3_fma3
    --------------------------------------------------------------
      For architectures: arch_null and arch_sse2_sse3_fma3 :
      In file "tests\math_fp_simdpp_-null.cc" at line 100 : 
      In test case "math_fp.fma" :
      Sequence number: 481
    ERROR: Vectors not equal: 
    A : [ 7ff8000000000000 ; 7ff8000000000000 ]
    A : [ 1.#QNAN ; 1.#QNAN ]
    B : [ fff8000000000000 ; fff8000000000000 ]
    B : [ -1.#IND ; -1.#IND ]
    --------------------------------------------------------------

All the following tests fail with the same error, if anyone has any clues on why this is happening that would be very useful.