blackdots_fix experimental branch update

This change is only to update the experimental "blackdots_fix" branch of Yafaray/Core (for the master branch I have sent a separate pull request with the complete updated fix to be aproved by DarkTide)

Now the domain checks are also performed when FAST-MATH=ON
Also, no need to differentiate acos() and acosf() as for C++ acos() it's an overloaded function and should work for float and double