ensure that the _mm_extract_epuXX helper macros actually return an unsigned type
ensure that the _mm_extract_epuXX helper macros actually return an unsigned type

Based on patch from Khouri Giordano. Thanks!

VcDevel/Vc,chr-engwer/Vc,chr-engwer/Vc,chr-engwer/Vc,VcDevel/Vc,VcDevel/Vc,VcDevel/Vc