Fade HRTF coefficients over 64 samples at most
Fade HRTF coefficients over 64 samples at most

This greatly improves HRTF performance since the dual-mix only applies to the
64-sample coefficient transition. So rather than doubling the full mix, it only
doubles 64 samples out of the full mix.

aaronmjacobs/openal-soft,aaronmjacobs/openal-soft